Pattern formation method

ABSTRACT

The photomask of this invention includes, on a transparent substrate, a semi-shielding portion having a transmitting property against exposing light, a transparent portion having a transmitting property against the exposing light and surrounded with the semi-shielding portion, and an auxiliary pattern surrounded with the semi-shielding portion and provided around the transparent portion. The semi-shielding portion and the transparent portion transmit the exposing light in an identical phase with respect to each other. The auxiliary pattern transmits the exposing light in an opposite phase with respect to the semi-shielding portion and the transparent portion and is not transferred through exposure.

RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.10/824,529, filed Apr. 15, 2004, claiming priority of Japaneseapplication Ser. No. 10/824,529, filed Jun. 24, 2003, the entirecontents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a photomask for use in fine patternformation in the fabrication of a semiconductor integrated circuitdevice, a pattern formation method using the photomask and a method forcreating mask data for the photomask.

Recently, there are increasing demands for thinning of circuit patternsin order to further increase the degree of integration of a large scaleintegrated circuit device (hereinafter referred to as the LSI) realizedby using semiconductors. Accordingly, thinning of an interconnectpattern used in a circuit or thinning of a contact hole pattern(hereinafter referred to as the contact pattern) for mutually connectingmultilayered interconnects having an insulating layer therebetween hasbecome very significant.

Now, the thinning of an interconnect pattern using a conventionaloptical exposure system will be described on the assumption that thepositive resist process is employed. In the positive resist process, aline pattern corresponds to a line-shaped resist film (a resist pattern)remaining correspondingly to an unexposed region of a resist afterexposure using a photomask and subsequent development. Also, a spacepattern corresponds to a resist removal portion (a resist removalpattern) corresponding to an exposed region of the resist. Furthermore,a contact pattern corresponds to a hole-shaped resist removal portionand can be regarded as a particularly fine space pattern. It is notedthat when the negative resist process is employed instead of thepositive resist process, the above-described definitions of a linepattern and a space pattern are replaced with each other.

In general, a fine pattern formation method using oblique incidentexposure (off-axis illumination) designated as super-resolution exposurehas been introduced for the thinning of an interconnect pattern. Thismethod is good for thinning a resist pattern corresponding to anunexposed region of a resist and has an effect to improve the depth offocus of dense patterns periodically and densely arranged. However, thisoblique incident exposure has substantially no effect to thin anisolated resist removal portion, and on the contrary, the contrast andthe depth of focus of an image (optical image) are degraded when it isemployed for an isolated resist removal portion. Therefore, the obliqueincident exposure has been positively employed in pattern formation inwhich a resist removal portion has a larger dimension than a resistpattern, such as gate pattern formation.

On the other hand, it is known that a small light source including nooblique incident component and having a low degree of coherence iseffectively used for forming an isolated fine resist removal portionlike a fine contact pattern. In this case, the pattern can be moreeffectively formed by using an attenuated phase-shifting mask. In anattenuated phase-shifting mask, a phase shifter is used instead of acompletely shielding portion as a shielding pattern for surrounding atransparent portion (an opening) corresponding to a contact pattern. Thephase shifter has very low transmittance of approximately 3 through 6%against exposing light, and causes phase inversion of 180 degrees in theexposing light with respect to light passing through the opening.

Herein, the transmittance is effective transmittance obtained byassuming that a transparent substrate has transmittance of 100% unlessotherwise mentioned. Also, a completely shielding film (a completelyshielding portion) means a shielding film (a shielding portion) havingeffective transmittance lower than 1%.

Now, the principle of a conventional pattern formation method using anattenuated phase-shifting mask will be described with reference to FIGS.32A through 32G.

FIG. 32A is a plan view of a photomask in which an opening correspondingto a contact pattern is formed in a chromium film formed on the masksurface as a completely shielding portion, and FIG. 32B shows theamplitude intensity obtained in a position corresponding to line AA′ oflight having passed through the photomask of FIG. 32A. FIG. 32C is aplan view of a photomask in which a chromium film corresponding to acontact pattern is formed in a phase shifter formed on the mask surface,and FIG. 32D shows the amplitude intensity obtained in a positioncorresponding to line AA′ of light having passed through the photomaskof FIG. 32C. FIG. 32E is a plan view of a photomask in which an openingcorresponding to a contact pattern is formed in a phase shifter formedon the mask surface (namely, an attenuated phase-shifting mask), andFIGS. 32F and 32G respectively show the amplitude intensity and thelight intensity obtained in a position corresponding to line AA′ oflight having passed through the photomask of FIG. 32E.

As shown in FIGS. 32B, 32D and 32F, the amplitude intensity of the lighthaving passed through the attenuated phase-shifting mask of FIG. 32E isa sum of the amplitude intensities of the lights having passed throughthe photomasks of FIGS. 32A and 32C. In other words, in the attenuatedphase-shifting mask of FIG. 32E, the phase shifter working as ashielding portion is formed not only so as to transmit light at lowtransmittance but also so as to cause an optical path difference (aphase difference) of 180 degrees in the light passing through theopening with respect to the light passing through the phase shifter.Therefore, as shown in FIGS. 32B and 32D, the light passing through thephase shifter has an amplitude intensity distribution in the oppositephase with respect to the light passing through the opening.Accordingly, when the amplitude intensity distribution of FIG. 32B andthe amplitude intensity distribution of FIG. 32D are synthesized witheach other, a phase boundary having amplitude intensity of 0 (zero) isobtained as a result of the phase change as shown in FIG. 32F. As aresult, as shown in FIG. 32G, at an end of the opening corresponding tothe phase boundary (hereinafter referred to as the phase end), the lightintensity, which is expressed as a square of the amplitude intensity, is0 (zero), and thus, a strongly dark part is formed. Therefore, in animage of the light having passed through the attenuated phase-shiftingmask of FIG. 32E, very high contrast can be realized around the opening.However, this improved contrast is obtained in light vertically enteringthe mask, and more specifically, light entering the mask from a smalllight source region with a low degree of coherence. On the other hand,such improved contrast cannot be obtained even around the opening(namely, in the vicinity of the phase boundary where the phase change iscaused) in employing the oblique incident exposure, such as exposuredesignated as annular illumination excluding a vertical incidentcomponent (an illumination component entering from the center of thelight source (along the normal direction of the mask)). Furthermore, ascompared with the case where the exposure is performed by using smalllight source with a low degree of coherence, the depth of focus isdisadvantageously smaller when the oblique incident exposure isemployed.

Moreover, in order to compensate the disadvantage of the attenuatedphase-shifting mask in the oblique incident exposure such as the annularillumination, a method in which a small opening that is not resolved,namely, an auxiliary pattern, is formed around an opening (correspondingto an isolated contact pattern) of the attenuated phase-shifting maskhas been proposed (for example, see Japanese Laid-Open PatentPublication No. 5-165194). Thus, a periodic light intensity distributioncan be obtained, thereby improving the depth of focus.

As described above, in the case where a fine resist removal pattern suchas a contact pattern is to be formed by the positive resist process, itis necessary to perform the exposure by using a combination of anattenuated phase-shifting mask and a small light source with a degree ofcoherence of approximately 0.5 or less, that is, illumination having avertical incident component alone. This method is very effective forforming a fine isolated contact pattern.

In accordance with recent increase of the degree of integration ofsemiconductor devices, it has become necessary to form, as not onlyinterconnect patterns but also contact patterns, isolated patterns andpatterns densely arranged at a pitch corresponding to the wavelength. Insuch a case, in order to realize a large depth of focus in the formationof densely arranged contact patterns, the oblique incident exposure iseffectively employed as in the formation of densely arrangedinterconnect patterns.

In other words, the oblique incident exposure is indispensable for theformation of dense interconnect patterns and dense contact patterns, butwhen the oblique incident exposure is employed, the contrast and thedepth of focus of isolated contact patterns and isolated space patternsbetween interconnects are largely degraded. This degradation of thecontrast and the depth of focus is more serious when an attenuatedphase-shifting mask is used for improving the resolution.

On the contrary, when a small light source with a low degree ofcoherence is used for forming isolated fine contact patterns andisolated fine space patterns between interconnects, it isdisadvantageously difficult to form dense patterns and fine linepatterns.

Accordingly, there is a reciprocal relationship between the optimumillumination conditions for isolated fine space patterns and the optimumillumination conditions for densely arranged patterns or fine linepatterns. Therefore, in order to simultaneously form fine resistpatterns and fine isolated resist removal patterns, trade-off isconsidered between the effect of a vertical incident component and theeffect of an oblique incident component of the light source. As aresult, a light source with an intermediate degree of coherence (ofapproximately 0.5 through 0.6) is used. In this case, however, both theeffects of the vertical incident component and the oblique incidentcomponent are cancelled, and therefore, it is difficult to realize ahigher degree of integration of semiconductor devices by simultaneouslythinning isolated line patterns or dense patterns and isolated spacepatterns.

It is noted that the aforementioned auxiliary pattern need to provideneeds to be provided in a position away from an opening corresponding toa contact pattern at least by a distance corresponding to the wavelengthof a light source (exposing light). Therefore, in the case whereopenings are arranged at a pitch ranging from the wavelength to a doubleof the wavelength, the auxiliary pattern cannot be used. In other words,the aforementioned method using the auxiliary pattern is not applicableto all arrangements ranging from the case where openings are arranged ata pitch substantially corresponding to the wavelength to the case wherean opening is isolated.

SUMMARY OF THE INVENTION

In consideration of the aforementioned conventional disadvantages, anobject of the invention is simultaneously thinning isolated spacepatterns and isolated line patterns or dense patterns.

In order to achieve the object, the photomask of this inventionincludes, on a transparent substrate, a semi-shielding portion having atransmitting property against exposing light; a transparent portionsurrounded with the semi-shielding portion and having a transmittingproperty against the exposing light; and an auxiliary pattern surroundedwith the semi-shielding portion and provided around the transparentportion. The semi-shielding portion and the transparent portion transmitthe exposing light in an identical phase with respect to each other, andthe auxiliary pattern transmits the exposing light in an opposite phasewith respect to the semi-shielding portion and the transparent portionand is not transferred through exposure.

In the photomask of this invention, the transparent portion ispreferably in the shape of a rectangle with a side smaller than(0.8×λ×M)/NA, wherein λ indicates a wavelength of the exposing light,and M and NA respectively indicate magnification and numerical apertureof a reduction projection optical system of a projection aligner. Inthis case, the auxiliary pattern is preferably a line-shaped pattern andhas a center line thereof in a position away from the center of thetransparent portion by a distance not less than (0.3×λ×M)/NA and notmore than (0.5×λ×M)/NA. Furthermore, the auxiliary pattern preferablyhas a width not less than (0.05×λ×M)/(NA×T^(0.5)) and not more than(0.2×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofthe auxiliary pattern to the transparent portion. Alternatively, theauxiliary pattern is preferably a line-shaped pattern and has a centerline thereof in a position away from the center of the transparentportion by a distance not less than (0.365×λ×M)/NA and not more than(0.435×λ×M)/NA. In this case, the auxiliary pattern preferably has awidth not less than (0.1×λ×M)/(NA×T^(0.5)) and not more than(0.15×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofthe auxiliary pattern to the transparent portion.

In the photomask of this invention, the transparent portion ispreferably in the shape of a line with a width smaller than(0.65×λ×M)/NA, wherein λ indicates a wavelength of the exposing light,and M and NA respectively indicate magnification and numerical apertureof a reduction projection optical system of a projection aligner. Inthis case, the auxiliary pattern is preferably a line-shaped pattern andhas a center line thereof in a position away from the center of thetransparent portion by a distance not less than (0.25×λ×M)/NA and notmore than (0.45×λ×M)/NA. Furthermore, the auxiliary pattern preferablyhas a width not less than (0.05×λ×M)/(NA×T^(0.5)) and not more than(0.2×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofthe auxiliary pattern to the transparent portion. Alternatively, theauxiliary pattern is preferably a line-shaped pattern and has a centerline thereof in a position away from the center of the transparentportion by a distance not less than (0.275×λ×M)/NA and not more than(0.425×λ×M)/NA. In this case, the auxiliary pattern preferably has awidth not less than (0.1×λ×M)/(NA×T^(0.5)) and not more than(0.15×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofthe auxiliary pattern to the transparent portion.

In the photomask of this invention, the auxiliary pattern preferablyincludes a first auxiliary pattern that is adjacent to a differentauxiliary pattern spaced by a given or smaller distance with thesemi-shielding portion sandwiched therebetween and a second auxiliarypattern that is not adjacent to a different auxiliary pattern spaced bythe given or smaller distance with the semi-shielding portion sandwichedtherebetween, and the first auxiliary pattern preferably has a smallerwidth than the second auxiliary pattern. In this case, the firstauxiliary pattern preferably includes a first pattern that is away fromthe adjacent different auxiliary pattern by a distance G1 and a secondpattern that is away from the adjacent different auxiliary pattern by adistance G2, and in the case where (0.5×λ×M)/NA>G1>G2, the secondpattern preferably has a smaller width than the first pattern, wherein λindicates a wavelength of the exposing light, and M and NA respectivelyindicate magnification and numerical aperture of a reduction projectionoptical system of a projection aligner. Furthermore, in this case, adifference between the width of the first pattern and the width of thesecond pattern is preferably in proportion to a difference between thedistance G1 and the distance G2.

In the photomask of this invention, in the case where the transparentportion is in the shape of a rectangle with a side smaller than(0.8×λ×M)/NA, the photomask preferably further includes, on thetransparent substrate, a second transparent portion adjacent to thetransparent portion and spaced by a given or smaller distance, and theauxiliary pattern preferably includes a first auxiliary pattern disposedin an area sandwiched between the transparent portion and the secondtransparent portion and a second auxiliary pattern disposed in the otherarea, and the first auxiliary pattern preferably has a smaller area thanthe second auxiliary pattern. In this case, the given distance ispreferably (1.3×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a line with a width smaller than(0.65×λ×M)/NA, the photomask preferably further includes, on thetransparent substrate, a second transparent portion adjacent to thetransparent portion and spaced by a given or smaller distance, and theauxiliary pattern preferably includes a first auxiliary pattern disposedin an area sandwiched between the transparent portion and the secondtransparent portion and a second auxiliary pattern disposed in the otherarea, and the first auxiliary pattern preferably has a smaller widththan the second auxiliary pattern. In this case, the given distance ispreferably (1.15×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a line with a width smaller than(0.65×λ×M)/NA, the photomask preferably further includes, on thetransparent substrate, a second transparent portion adjacent to thetransparent portion and spaced by a given or smaller distance, and theauxiliary pattern preferably includes a first auxiliary pattern disposedin an area sandwiched between the transparent portion and the secondtransparent portion and a second auxiliary pattern disposed in the otherarea, and the first auxiliary pattern preferably has a smaller area thanthe second auxiliary pattern. In this case, the given distance ispreferably (1.15×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a rectangle with a side smaller than(0.8×λ×M)/NA, the transparent portion is preferably close to a differenttransparent portion spaced by a distance of a given range at least alonga first direction and is not close to a different transparent portionspaced by a distance of the given range at least along a seconddirection, the auxiliary pattern preferably includes a first auxiliarypattern disposed around the transparent portion along the firstdirection and a second auxiliary pattern disposed around the transparentportion along the second direction, and the first auxiliary pattern ispreferably farther from the transparent portion than the secondauxiliary pattern. In this case, the given range is preferably from(1.15×λ×M)/NA to (1.45×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a rectangle with a side smaller than(0.8×λ×M)/NA, the transparent portion is preferably close to a differenttransparent portion spaced by a distance of a given range at least alonga first direction and is not close to a different transparent portionspaced by a distance of the given range at least along a seconddirection, the auxiliary pattern preferably includes a first auxiliarypattern disposed around the transparent portion along the firstdirection and a second auxiliary pattern disposed around the transparentportion along the second direction, and the first auxiliary pattern ispreferably closer to the transparent portion than the second auxiliarypattern. In this case, the given range is preferably from (0.85×λ×M)/NAto (1.15×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a line with a width smaller than(0.65×λ×M)/NA, the transparent portion is preferably close to adifferent transparent portion spaced by a distance of a given range atleast along a first direction and is not close to a differenttransparent portion spaced by a distance of the given range at leastalong a second direction, the auxiliary pattern preferably includes afirst auxiliary pattern disposed around the transparent portion alongthe first direction and a second auxiliary pattern disposed around thetransparent portion along the second direction, and the first auxiliarypattern is preferably farther from the transparent portion than thesecond auxiliary pattern. In this case, the given range is preferablyfrom (1.0×λ×M)/NA to (1.3×λ×M)/NA.

In the photomask of this invention, in the case where the transparentportion is in the shape of a line with a width smaller than(0.65×λ×M)/NA, the transparent portion is preferably close to adifferent transparent portion spaced by a distance of a given range atleast along a first direction and is not close to a differenttransparent portion spaced by a distance of the given range at leastalong a second direction, the auxiliary pattern preferably includes afirst auxiliary pattern disposed around the transparent portion alongthe first direction and a second auxiliary pattern disposed around thetransparent portion along the second direction, and the first auxiliarypattern is preferably closer to the transparent portion than the secondauxiliary pattern. In this case, the given range is preferably from(0.7×λ×M)/NA to (1.0×λ×M)/NA.

In the photomask of this invention, the transparent portion ispreferably in the shape of a line, the auxiliary pattern is preferablydisposed in parallel to the transparent portion along a line directionof the transparent portion, and the transparent portion preferably has aline end protruded beyond the auxiliary pattern by a given or largerdimension along the line direction. In this case, the given dimension ispreferably (0.03×λ×M)/NA, wherein λ indicates a wavelength of theexposing light, and M and NA respectively indicate magnification andnumerical aperture of a reduction projection optical system of aprojection aligner.

In the photomask of this invention, the transparent portion ispreferably in the shape of a line, the auxiliary pattern preferablyincludes a pair of first auxiliary patterns disposed in parallel to thetransparent portion along a line direction of the transparent portionand sandwiching a line center part of the transparent portion and a pairof second auxiliary patterns disposed in parallel to the transparentportion along the line direction and sandwiching a line end part of thetransparent portion, and a distance between the pair of second auxiliarypatterns is preferably larger by a given or larger dimension than adistance between the pair of first auxiliary patterns. In this case,each of the pair of second auxiliary patterns preferably has a lengthalong the line direction of (0.03×λ×M)/NA or more, wherein λ indicates awavelength of the exposing light, and M and NA respectively indicatemagnification and numerical aperture of a reduction projection opticalsystem of a projection aligner. Also, the given degree is preferably(0.03×λ×M)/NA or more.

In the photomask of this invention, the transparent portion ispreferably formed by exposing the transparent substrate, the auxiliarypattern is preferably formed by depositing, on the transparentsubstrate, a first phase shift film that causes, in the exposing light,a phase difference in an opposite phase with respect to the transparentportion, and the semi-shielding portion is preferably formed bydepositing, on the first phase shift film, a second phase shift filmthat causes, in the exposing light, a phase difference in an oppositephase with respect to the first phase shift film.

In the photomask of this invention, the transparent portion ispreferably formed by exposing the transparent substrate, the auxiliarypattern is preferably formed by trenching the transparent substrate by adepth for causing, in the exposing light, a phase difference in anopposite phase with respect to the transparent portion, and thesemi-shielding portion is preferably formed by depositing, on thetransparent substrate, a semi-shielding film that transmits the exposinglight in an identical phase with respect to the transparent portion.

In the photomask of this invention, the transparent portion ispreferably formed by exposing the transparent substrate, the auxiliarypattern is preferably formed by trenching the transparent substrate by adepth for causing, in the exposing light, a phase difference in anopposite phase with respect to the transparent portion, and thesemi-shielding portion is preferably formed by depositing, on thetransparent substrate, a metal thin film that transmits the exposinglight in an identical phase with respect to the transparent portion.

In the photomask of this invention, the auxiliary pattern is preferablyformed by exposing the transparent substrate, the transparent portion ispreferably formed by trenching the transparent substrate by a depth forcausing, in the exposing light, a phase difference in an opposite phasewith respect to the auxiliary pattern, and the semi-shielding portion ispreferably formed by depositing, on the transparent substrate, a phaseshift film that causes, in the exposing light, a phase difference in anopposite phase with respect to the auxiliary pattern.

The pattern formation method of this invention uses a photomask of thisinvention, and the pattern formation method includes the steps offorming a resist film on a substrate; irradiating the resist film withthe exposing light through the photomask, and forming a resist patternby developing the resist film after irradiation with the exposing light.

The mask data creation method of this invention is employed for creatingmask data for a photomask including a mask pattern formed on atransparent substrate and a transparent portion of the transparentsubstrate where the mask pattern is not formed. Specifically, the maskdata creation method includes the steps of determining an internaldistance and a width of outline shifters on the basis of a desiredexposed region of a resist formed by irradiating the resist withexposing light through the photomask; providing the transparent portioninside the outline shifters; setting the transparent portion as a CDadjustment pattern; providing a semi-shielding portion for transmittingthe exposing light in an identical phase with respect to the transparentportion in such a manner that the transparent portion and the outlineshifters are surrounded with the semi-shielding portion; setting theoutline shifters as phase shifters that transmit the exposing light inan opposite phase with respect to the transparent portion; predicting,through simulation, a dimension of a resist pattern formed by using themask pattern including the phase shifters and the semi-shieldingportion; and when the predicted dimension of the resist pattern does notaccord with a desired dimension, deforming the mask pattern by deformingthe CD adjustment pattern. In this method, the step of determining aninternal distance and a width of outline shifters preferably includes asub-step of changing the width of the outline shifters in accordancewith a distance between the outline shifters. Furthermore, the step ofdetermining an internal distance and a width of outline shifterspreferably includes a sub-step of changing the internal distance of theoutline shifters in accordance with a close relationship between desiredexposed regions.

According to this invention, contrast of a light intensity distributionbetween a transparent portion and an auxiliary pattern can be emphasizedby utilizing mutual interference between light passing through thetransparent portion and light passing through the auxiliary pattern.Also, this effect to emphasize the contrast can be attained also in thecase where a fine isolated space pattern corresponding to thetransparent portion is formed by, for example, the positive resistprocess using the oblique incident exposure. Accordingly, an isolatedspace pattern and an isolated line pattern or dense patterns can besimultaneously thinned by employing the oblique incident exposure.Furthermore, even in the case where complicated and fine space patternsare close to each other, a pattern with a desired dimension can besatisfactorily formed.

Herein, having a transmitting property against exposing light meanshaving transmittance sufficiently high for sensitizing a resist, andhaving a shielding property against exposing light means having too lowtransmittance to sensitize a resist. Furthermore, an identical phasemeans a phase difference not less than (−30+360×n) degrees and not morethan (30+360×n) degrees, and an opposite phase means a phase differencenot less than (150+360×n) degrees and not more than (210+360×n) degrees(wherein n is an integer).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G are diagrams for explaining theprinciple of an outline enhancement method of this invention;

FIG. 2A is a plan view of a photomask according to Embodiment 1 of theinvention and FIG. 2B is a diagram of a light intensity distributionformed on a wafer through exposure using the photomask of FIG. 2A;

FIG. 3A is a graph of a result of simulation performed for obtaining acombination of a dimension W, a distance PW and a width d for attainingpeak intensity Io of 0.25 in the photomask of FIG. 2A, FIG. 3B is adiagram of a result of simulation for a depth of focus in which acontact hole with a size of 100 nm is formed by using a mask patternhaving the combination of the distance PW, the dimension W and the widthd shown in the graph of FIG. 3A, and FIG. 3C is a diagram of a result ofsimulation for an exposure margin in which a contact hole with a size of100 nm is formed by using the mask pattern having the combination of thedistance PW, the dimension W and the width d shown in the graph of FIG.3A;

FIGS. 4A, 4C and 4E are diagrams of results of simulation for a depth offocus in which a contact hole with a size of 100 nm is formed by usingthe photomask of Embodiment 1 of the invention, and FIGS. 4B, 4D and 4Fare diagrams of results of simulation for an exposure margin in which acontact hole with a size of 100 nm is formed by using the photomask ofEmbodiment 1 of the invention;

FIGS. 5A, 5B, 5C and 5D are diagrams for showing variations of the planestructure of the photomask of Embodiment 1;

FIGS. 6A, 6B, 6C and 6D are diagrams for showing variations of thecross-sectional structure of the photomask of Embodiment 1;

FIG. 7A is a plan view of a photomask according to a modification ofEmbodiment 1 and FIG. 7B is a diagram of a light intensity distributionformed on a wafer through exposure using the photomask of FIG. 7A;

FIG. 8A is a graph of a result of simulation performed for obtaining amask structure for attaining the peak intensity Io of 0.25 in thephotomask of the modification of Embodiment 1, FIG. 8B is a diagram of aresult of simulation for a depth of focus in which a space pattern witha width of 100 nm is formed by using a photomask having the maskstructure shown in the graph of FIG. 8A, and FIG. 8C is a diagram of aresult of simulation for an exposure margin in which a space patternwith a width of 100 nm is formed by using the photomask having the maskstructure shown in the graph of FIG. 8A;

FIG. 9 is a plan view of a photomask according to Embodiment 2 of theinvention;

FIG. 10A is a plan view of a photomask used in simulation performed forconfirming the effect of the photomask according to Embodiment 2 or 3 ofthe invention, and FIG. 10B is a diagram of a profile of a lightintensity distribution formed through exposure using the photomask ofFIG. 10A;

FIGS. 11A, 11B and 11C are diagrams of results of simulation performedfor confirming the effect of the photomask of Embodiment 2;

FIGS. 12A and 12B are diagrams for explaining the reason why the widthof a phase shifter provided between transparent portions is preferablyreduced in the photomask of Embodiment 2 in forming dense holes in whicha distance between the centers of the transparent portions is 1.3×λ/NAor less;

FIGS. 13A, 13B and 13C are diagrams of variations of the plane structureof the photomask of Embodiment 2;

FIGS. 14A and 14B are diagrams of other variations of the planestructure of the photomask of Embodiment 2;

FIG. 15 is a plan view of a photomask according to a modification ofEmbodiment 2;

FIGS. 16A, 16B and 16C are diagrams of variations of the plane structureof the photomask of the modification of Embodiment 2;

FIG. 17 is a plan view of a photomask according to Embodiment 3 of theinvention;

FIGS. 18A, 18B, 18C and 18D are diagrams of results of simulationperformed for confirming the effect of the photomask of Embodiment 3;

FIG. 19 is a plan view of a photomask according to a modification ofEmbodiment 3;

FIGS. 20A and 20B are diagrams of results of simulation performed forconfirming the effect of the photomask of the modification of Embodiment3;

FIG. 21A is a plan view of a photomask according to Embodiment 4 of theinvention and FIG. 21B is a diagram of a result of pattern formationsimulation using the photomask of FIG. 21A;

FIGS. 22A, 22B and 22C are diagrams of results of simulation performedfor confirming the effect of the photomask of Embodiment 4;

FIG. 23A is a plan view of a photomask according to a modification ofEmbodiment 4 and FIG. 23B is a diagram of a result of pattern formationsimulation using the photomask of FIG. 23A;

FIGS. 24A, 24B and 24C are diagrams of results of simulation performedfor confirming the effect of the photomask of the modification ofEmbodiment 4;

FIGS. 25A, 25B, 25C and 25D are cross-sectional views for showingprocedures in a pattern formation method according to Embodiment 5 ofthe invention;

FIG. 26A is a diagram for showing the shape of a general exposure lightsource and FIGS. 26B, 26C and 26D are diagrams for showing the shapes ofoblique incident exposure light sources;

FIGS. 27A, 27B, 27C, 27D and 27E are diagrams for explaining a result ofsimulation performed for obtaining the dependency of an exposurecharacteristic of the photomask of this invention on the diameter ofannular illumination;

FIG. 28 is a plan view of a photomask used in explanation of a mask datacreation method according to Embodiment 6 of the invention;

FIG. 29 is a flowchart of the mask data creation method of Embodiment 6;

FIGS. 30A, 30B and 30C are diagrams for showing specific examples ofmask patterns obtained in respective procedures in the mask datacreation method of Embodiment 6;

FIGS. 31A and 31B are diagrams for showing specific examples of maskpatterns obtained in respective procedures in the mask data creationmethod of Embodiment 6; and

FIGS. 32A, 32B, 32C, 32D, 32E, 32F and 32G are diagrams for explainingthe principle of a conventional pattern formation method using anattenuated phase-shifting mask.

DETAILED DESCRIPTION OF THE INVENTION

(Prerequisites)

Prerequisites for describing preferred embodiments of the invention willbe first described.

Since a photomask is generally used in a reduction projection typealigner, it is necessary to consider a reduction ratio in arguing apattern dimension on the mask. However, in order to avoid confusion, inthe description of each embodiment below, when a pattern dimension on amask is mentioned in correspondence to a desired pattern to be formed(such as a resist pattern), a value obtained by converting the patterndimension by using a reduction ratio (magnification) is used unlessotherwise mentioned. Specifically, also in the case where a resistpattern with a width of 100 nm is formed by using a mask pattern with awidth of M×100 nm in a 1/M reduction projection system, the width of themask pattern and the width of the resist pattern are both described as100 nm.

Also, in each embodiment of the invention, M and NA respectivelyindicate a reduction ratio and numerical aperture of a reductionprojection optical system of an aligner and λ indicates the wavelengthof exposing light unless otherwise mentioned.

Moreover, pattern formation is described in each embodiment on theassumption that the positive resist process for forming a resist patterncorrespondingly to an unexposed region of a resist is employed. In thecase where the negative resist process is employed instead of thepositive resist process, since an unexposed region of a resist isremoved in the negative resist process, a resist pattern of the positiveresist process is replaced with a space pattern.

Moreover, a photomask described in each embodiment is assumed to be atransmission mask. In the case where the photomask is applied to areflection mask, since a transparent region and a shielding region of atransmission mask respectively correspond to a reflection region and anon-reflection region, the transmission phenomenon of the transmissionmask is replaced with the reflection phenomenon. Specifically, atransparent portion or a transparent region of a transmission mask isreplaced with a reflection portion or a reflection region, and ashielding portion is replaced with a non-reflection portion.Furthermore, a region partially transmitting light in a transmissionmask is replaced with a portion partially reflecting light, and thetransmittance is replaced with reflectance.

(Outline Enhancement Method)

First, a resolution improving method by using a photomask devised by thepresent inventor for realizing the present invention, that is, an“outline enhancement method” for improving the resolution of an isolatedspace pattern, will be described.

The following description is given in assuming formation of a spacepattern by the positive resist process. It is noted that the “outlineenhancement method” has the principle holding good regardless of theshape of a pattern as far as the pattern is a fine space pattern formedby the positive resist process. Also, the “outline enhancement method”is similarly applicable to the negative resist process by replacing afine space pattern (resist removal pattern) of the positive resistprocess with a fine pattern (resist pattern).

FIGS. 1A through 1G are diagrams for explaining the principle foremphasizing the contrast of a transferred image of light in exposureperformed for forming a space pattern.

FIG. 1A is a plan view of a photomask in which an opening (i.e., atransparent portion) corresponding to a space pattern is surrounded witha semi-shielding portion with given transmittance against exposinglight, and FIG. 1B shows the amplitude intensity obtained in a positioncorresponding to line AB of light having passed through the photomask ofFIG. 1A.

FIG. 1C is a plan view of a photomask in which a phase shifter isprovided around an opening and a completely shielding portion isprovided in the remaining area, and FIG. 1D shows the amplitudeintensity obtained in a position corresponding to line AB of lighthaving passed through the photomask of FIG. 1C. Since the amplitudeintensity shown in FIG. 1D is obtained with respect to the light passingthrough the phase shifter, it is in the opposite phase to the lightamplitude intensity shown in FIG. 1B.

FIG. 1E is a plan view of a photomask in which an opening correspondingto a space pattern and a phase shifter provided around the opening aresurrounded with a semi-shielding portion with given transmittanceagainst exposing light, and FIGS. 1F and 1G respectively show theamplitude intensity and the light intensity (which is a square of theamplitude intensity) obtained in a position corresponding to line AB oflight having passed through the photomask of FIG. 1E. The photomask ofFIG. 1E is obtained by providing a phase shifter around the opening ofthe photomask of FIG. 1A. Among these photomasks, the photomask of FIG.1E is an example of a photomask according to the present invention forrealizing the “outline enhancement method” (hereinafter referred to asthe outline enhancement mask).

In the photomask of FIG. 1A or 1E, there is a relationship of anidentical phase between light passing through the semi-shielding portionand light passing through the opening (specifically, a relationship thata phase difference between these lights is not less than (−30+360×n)degrees and not more than (30+360×n) degrees (wherein n is an integer)).Also, in the photomask of FIG. 1E, there is a relationship of theopposite phases between light passing through the phase shifter andlight passing through the opening (specifically, a relationship that aphase difference between these lights is not less than (150+360×n)degrees and not more than (210+360×n) degrees (wherein n is aninteger)).

A transferred image of the light having passed through the outlineenhancement mask of FIG. 1E is emphasized through the followingprinciple: The structure of the photomask of FIG. 1E is obtained bycombining the photomasks of FIGS. 1A and 1C. Accordingly, as shown inFIGS. 1B, 1D and 1F, the amplitude intensity of the light having passedthrough the photomask of FIG. 1E has a distribution obtained bycombining the amplitude intensities of the lights respectively havingpassed through the photomasks of FIGS. 1A and 1C. At this point, as isunderstood from FIG. 1F, the light having passed through the phaseshifter provided around the opening in the photomask of FIG. 1E canpartially cancel the lights respectively having passed through theopening and the semi-shielding portion. Accordingly, when the intensityof the light passing through the phase shifter is adjusted so as tocancel light passing through a periphery of the opening in the photomaskof FIG. 1E, a dark part in which the light intensity obtained in theperiphery of the opening is reduced to approximately 0 (zero) can beformed in the light intensity distribution as shown in FIG. 1G.

In the photomask of FIG. 1E, the light passing through the phase shifterstrongly cancels the light passing through the periphery of the openingand weakly cancels light passing through the center of the opening. As aresult, as shown in FIG. 1G, it is possible to attain an effect that thegradient of the profile of the light intensity distribution changingfrom the center of the opening to the periphery of the opening can beincreased. Accordingly, the intensity distribution of the light passingthrough the photomask of FIG. 1E achieves a sharp profile, resulting informing an image with high contrast.

This is the principle of the emphasis of an optical image (an image oflight intensity) according to the present invention. Specifically, sincethe phase shifter is provided along the outline of the opening in themask composed of the semi-shielding portion with low transmittance, avery dark part corresponding to the outline of the opening can be formedin the light intensity image formed by using the photomask of FIG. 1A.Accordingly, a light intensity distribution in which contrast betweenthe light intensity obtained in the opening and the light intensityobtained in the periphery of the opening is emphasized can be attained.Herein, a method for emphasizing an image through this principle isdesignated as the “outline enhancement method”, and a photomask forrealizing this principle is designated as the “outline enhancementmask”.

When the outline enhancement method is compared with the conventionalprinciple of an attenuated phase shifter (see FIGS. 32A through 32G),the outline enhancement method is different from the conventionalprinciple in mechanism for forming the dark part in the periphery of theopening in the light intensity distribution. As is understood fromcomparison between FIG. 1F and FIG. 32F, the dark part in the amplitudeintensity distribution is formed by the phase boundary in theconventional attenuated phase shifter. In contrast, in the outlineenhancement method, the dark part in the amplitude intensitydistribution is formed as a result of periodical change of the amplitudeintensity in the identical phase. Also, the dark part formed by thephase boundary in the conventional attenuated phase shifter cannot besufficiently emphasized through the oblique incident exposure, andtherefore, the conventional attenuated phase shifter should be combinedwith exposure using a small light source with a low degree of coherence.In contrast, the dark part formed through the periodical change of theamplitude intensity in the identical phase in the outline enhancementmethod is equivalent to a dark part formed by using a general pattern inwhich general transparent portions and shielding portions areperiodically arranged, and therefore, the contrast of the lightintensity distribution can be emphasized by combining the outlineenhancement method and the oblique incident exposure. In other words,the effect of the outline enhancement method can be more remarkablyexhibited when combined with the oblique incident exposure.

In the outline enhancement mask, the maximum transmittance of thesemi-shielding portion is preferably approximately 15% for preventingthe thickness of a resist film from reducing in pattern formation or foroptimizing the resist sensitivity. In other words, the transmittance ofthe semi-shielding portion is preferably approximately 15% or less inthe outline enhancement mask. Furthermore, the semi-shielding portionneeds to have a property to partially transmit light, and in order tosufficiently attain the effect to substantially transmit light, thetransmittance of the semi-shielding portion is preferably at least 3% ormore and more preferably 6% or more. Accordingly, the optimumtransmittance of the semi-shielding portion of the outline enhancementmask is not less than 6% and not more than 15%.

Although the outline enhancement method has been described on theassumption that the phase shifter is provided on the boundary betweenthe semi-shielding portion and the transparent portion (i.e., theopening) surrounded with the semi-shielding portion, it is not alwaysnecessary to provide the phase shifter on the boundary. Specifically, asfar as the phase shifter is provided in a position for enablinginterference with light passing through the transparent portion throughthe principle of the outline enhancement method, the light having passedthrough the periphery of the transparent portion can be cancelled.Accordingly, the phase shifter may be provided in a position away from,for example, each side of a rectangular opening disposed in thesemi-shielding portion as a pattern parallel to each side. However, inorder to effectively utilize the outline enhancement method, the phaseshifter is preferably provided in a position away from the opening by adistance not more than 0.5×λ/NA, which is a distance for causing lightinterference. Furthermore, when the semi-shielding portion with asufficient width (i.e., a width not less than λ/NA) is provided outsidethe phase shifter surrounding the transparent portion, a completelyshielding portion may be provided outside the semi-shielding portion.

Now, preferred embodiments each for realizing a desired pattern by usinga mask obtained on the basis of the principle of the outline enhancementmethod will be described.

EMBODIMENT 1

A photomask according to Embodiment 1 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 2A is a plan view of the photomask of Embodiment 1 (whereas atransparent substrate is perspectively shown, and this applies tosimilar drawings mentioned below). The photomask of this embodiment isused for forming a fine contact pattern.

As shown in FIG. 2A, a semi-shielding portion 101 covering asufficiently large area is formed on a transparent substrate 100. Also,an opening pattern corresponding to a transparent portion 102 is formedin the semi-shielding portion 101 in a position corresponding to adesired contact pattern to be formed on a wafer through exposure.Furthermore, auxiliary patterns corresponding to phase shifters 103 areprovided around the transparent portion 102 with the semi-shieldingportion 101 sandwiched therebetween, for example, so as to be parallelto respective sides of the transparent portion 102 in a square shape ora rectangular shape. In other words, the phase shifters 103 are providedso as to surround the transparent portion 102.

In this embodiment, the semi-shielding portion 101 partially transmitslight, and there is a relationship of the identical phase between lightpassing through the semi-shielding portion 101 and light passing throughthe transparent portion 102 (more specifically, a relationship that aphase difference between these lights is not less than (−30+360×n)degrees and not more than (30+360×n) degrees (wherein n is an integer)).Also, the semi-shielding portion 101 preferably has transmittancesufficiently low not to sensitize a resist, and specifically, thesemi-shielding portion 101 has transmittance of 15% or less. On theother hand, in order to allow the semi-shielding portion 101 to have adifferent property from the transparent portion 102, the semi-shieldingportion 101 has transmittance preferably not less than 3% and morepreferably not less than 6%. In particular, in forming a contact hole,the optimum transmittance of the semi-shielding portion 101 isapproximately 9%.

On the other hand, the phase shifter 103 transmits light, and there is arelationship of the opposite phase between light passing through thephase shifter 103 and light passing through the transparent portion 102(specifically, a relationship that a phase difference between theselights is not less than (150+360×n) degrees and not more than(210+360×n) degrees (wherein n is an integer)). It is noted that in allembodiments mentioned below and including this embodiment, the phaseshifter is regarded to have transmittance equivalent to that of thetransparent portion (the transparent substrate) unless otherwisementioned but the transmittance of the phase shifter is not hereinparticularly specified. However, in order to utilize the characteristicof the phase shifter to transmit light in the opposite phase, thetransmittance of the phase shifter is preferably larger than at leastthe transmittance of the semi-shielding portion. Also, in order toefficiently realize the principle of the outline enhancement method, thetransmittance of the phase shifter is preferably 50% or more.

Furthermore, assuming that an optical system using the photomask of FIG.2A has exposure wavelength λ and numerical aperture NA, in the mostpreferable structure for forming a fine contact hole, a distance betweenthe center lines of the phase shifters 103 opposing each other with thetransparent portion 102 sandwiched therebetween is 0.8×λ/NA as describedin detail later. In other words, each phase shifter 103 is optimallyprovided in a position where the center line of the phase shifter 103 isaway from the center of the transparent portion 102 by a distance of0.4×λ/NA. Furthermore, when the transmittance of the phase shifter 103is set to be the same as the transmittance of the transparent portion102, the width of the phase shifter 103 is optimally set to 0.15×λ/NA.

Also, in each of all the embodiments described below, the aforementioneddescription is applied to a semi-shielding portion, a transparentportion and a phase shifter (an auxiliary pattern).

Now, a good pattern formation characteristic of the photomask with theaforementioned structure exhibited in forming a fine contact hole, andmore particularly, in forming a pattern with a dimension of 0.4×λ/NA orless will be described on the basis of a result of simulation.

It is assumed in the simulation that the transparent portion 102 is inthe shape of a square having a side dimension W, that each phase shifter103 is a rectangular pattern with a width d and that the center line ofeach phase shifter 103 is disposed in a position away from the center ofthe transparent portion 102 by a distance PW in the photomask of FIG.2A. In other words, a distance between a pair of opposing phase shifters103 provided with the transparent portion 102 sandwiched therebetween is2×PW. Also, it is assumed that the semi-shielding portion 101 working asthe background has transmittance of 9%. Under these conditions, thelight intensity is simulated with respect to various combinations of thedimension W, the distance PW and the width d. In this simulation,optical calculation is carried out on the assumption that the exposureis carried out with a wavelength λ of 193 nm and the numerical apertureNA of 0.7. Furthermore, ⅔ annular illumination having the outer diameterwith a degree of coherence of 0.8 and the inner diameter with a degreeof coherence of 0.53 is assumed to be used.

FIG. 2B shows a light intensity distribution formed on a wafer (in aposition corresponding to line AB of FIG. 2A) through the exposure usingthe photomask of FIG. 2A. The light intensity distribution of FIG. 2Bhas a profile with a peak in a position corresponding to the center ofthe transparent portion 102. In this case, it is necessary for the peakintensity Io to be not less than a given value in order to sensitize aresist corresponding to the center of the transparent portion 102. Thepeak intensity Io necessary for sensitizing the resist depends upon theused resist material, and it has been experimentally found that the peakintensity Io necessary for forming a fine contact hole with a size of0.4×λ/NA or less is approximately 0.25. It is noted that light intensitymentioned herein is expressed as relative light intensity obtained byassuming that the light intensity of the exposing light is 1 unlessotherwise mentioned.

FIG. 3A shows the combinations of the dimension W, the distance PW andthe width d for attaining the peak intensity Io of 0.25 in the photomaskof FIG. 2A obtained as a result of the simulation. Specifically, FIG. 3Ais obtained by plotting the dimension W of the transparent portion 102for attaining the peak intensity Io of 0.25 against the distance 2×PWbetween the center lines of the pair of opposing phase shifters 103provided with the transparent portion 102 sandwiched therebetween(hereinafter simply referred to as the shifter center line distance).Also, FIG. 3A shows the relationships between the shifter center linedistance 2×PW and the dimension W respectively obtained when the width dof the phase shifter 103 is 20 nm, 30 nm, 40 nm, 50 nm and 60 nm. Inother words, the light intensity distribution having the peak intensityIo of 0.25 can be formed by employing any of all the combinations of thedistance PW, the dimension W and the width d shown in the graph of FIG.3A. Furthermore, among these combinations, one having the maximum depthof focus or the maximum exposure margin corresponds to a mask structurehaving a good pattern formation characteristic.

FIG. 3B shows a result of simulation for the depth of focus in which acontact hole with a size of 100 nm is formed by using a mask patternhaving the combination of the distance PW, the dimension W and the widthd shown in the graph of FIG. 3A. In FIG. 3B, the abscissa indicates theshifter center line distance 2×PW and the value of the depth of focus isplotted by using the width d as a parameter on the ordinate. As shown inFIG. 3B, with respect to all the values of the width d, the depth offocus has the maximum value when the shifter center line distance 2×PWhas a value in the vicinity of 0.8×λ/NA (=approximately 220 nm). At thispoint, the depth of focus means the width of a range of a focus positionfor attaining, in forming a contact hole with a target size of 100 nm,dimension variation of 10% or less of the target size.

Similarly, FIG. 3C shows a result of simulation for the exposure marginin which a contact hole with a size of 100 nm is formed by using a maskpattern having the combination of the distance PW, the dimension W andthe width d shown in the graph of FIG. 3A. In FIG. 3C, the abscissaindicates the shifter center line distance 2×PW and the value of theexposure margin is plotted by using the width d as a parameter on theordinate. As shown in FIG. 3C, regardless of the value of the width d,the exposure margin has the maximum value when the shifter center linedistance 2×PW has a value in the vicinity of 0.8×λ/NA (=approximately220 nm). At this point, the exposure margin means a ratio in percentageof the width of a range of exposure energy for attaining, in forming acontact hole with a target size of 100 nm, dimension variation of 10% orless of the target size to the value of exposure energy for realizing acontact hole with a size of 100 nm.

Specifically, in the photomask of FIG. 2A, no matter what value thewidth d of the phase shifter has, the shifter center line distance 2×PWis approximately 0.8×λ/NA when the depth of focus for forming a finecontact pattern is optimized. Also when the exposure margin isoptimized, the shifter center line distance 2×PW is approximately0.8×λ/NA. At this point, that the optimum value of the shifter centerline distance 2×PW does not depend upon the width d of the phase shiftermeans that the optimum value does not depend upon the transmittance ofthe phase shifter either.

In phase shifters having the shifter center line distance 2×PW of0.8×λ/NA, both of the depth of focus and the exposure margin have largevalues when the width d of each phase shifter is approximately 0.15×λ/NA(=40 nm). On the basis of these results, it is found that a maskstructure in which the phase shifters 103 are provided to oppose eachother with the transparent portion 102 sandwiched therebetween, eachphase shifter 103 has a width of 0.15×λ/NA and the shifter center linedistance is 0.8×λ/NA is good at fine contact hole formation.

Furthermore, referring to the graphs of FIGS. 3B and 3C in detail, it isunderstood that a large depth of focus and a large exposure margin canbe attained as far as the width d of the phase shifter is not less than0.05×λ/NA and not more than 0.2×λ/NA. Also, it is understood that alarge depth of focus and a large exposure margin can be attained as faras the shifter center line distance is not less than 0.6×λ/NA and notmore than λ/NA (namely, the distance between the center line of thephase shifter and the center of the transparent portion is not less than0.3×λ/NA and not more than 0.5×λ/NA). Furthermore, in order to attain adepth of focus and an exposure margin approximate to their maximumvalues, the width d of the phase shifter is preferably not less than0.1×λ/NA and not more than 0.15×λ/NA, and the shifter center linedistance is preferably not less than 0.73×λ/NA and not more than0.87×λ/NA (namely, the distance between the center line of the phaseshifter and the center of the transparent portion is preferably not lessthan 0.365×λ/NA and not more than 0.435×λ/NA).

The results shown in FIGS. 3B and 3C are described as data obtained inthe exemplified case where the numerical aperture NA is 0.7, and resultsobtained through simulation where the numerical aperture NA is 0.6 and0.8 are shown in FIGS. 4A through 4D. FIGS. 4A and 4B show the resultsof the simulation where the numerical aperture NA is 0.6, and as shownin these graphs, the depth of focus and the exposure margin both havethe maximum values when the shifter center line distance 2×PW isapproximately 0.8×λ/NA (=approximately 250 nm). Also, FIGS. 4C and 4Dshow the results of the simulation where the numerical aperture NA is0.8, and as shown in these graphs, the depth of focus and the exposuremargin both have the maximum values when the shifter center linedistance 2×PW is approximately 0.8×λ/NA (=approximately 190 nm). Thus,the aforementioned optimum mask structure does not depend upon the valueof the numerical aperture NA.

Furthermore, the results shown in FIGS. 3B and 3C are obtained throughthe simulation where the semi-shielding portion has transmittance of 9%,and results of simulation where the semi-shielding portion hastransmittance of 6% are shown in FIGS. 4E and 4F. As shown in FIGS. 4Eand 4F, similarly to the case where the semi-shielding portion hastransmittance of 9%, the depth of focus and the exposure margin bothhave the maximum values when the shifter center line distance 2×PW isapproximately 0.8×λ/NA (=approximately 250 nm). Thus, the aforementionedoptimum mask structure does not depend upon the transmittance of thesemi-shielding portion.

As described so far, assuming that the exposure wavelength is λ and thenumerical aperture of the exposure system is NA, a photomask usable forforming a fine contact hole pattern with the maximum depth of focus andthe maximum exposure margin can be obtained in the structure in which anopening corresponding to a transparent portion is provided in asemi-shielding portion, each of phase shifters surrounding the openinghas a width d of 0.15×λ/NA and each phase shifter is provided so as tohave its center line away from the center of the transparent portion bya distance of 0.4×λ/NA. It is noted that the phase shifter hasequivalent transmittance to the transparent portion and the maximumvalue of the width d of the phase shifter is 0.15×λ/NA in thisembodiment. In the case where the phase shifter has transmittancedifferent from that of the transparent portion, namely, in the casewhere the effective relative transmittance of the phase shifter (theauxiliary pattern) to the transparent portion is not 1, the width of thephase shifter is changed in accordance with the relative transmittancefor realizing an equivalent transmitting property. Specifically,assuming that the relative transmittance is T, the width d of the phaseshifter is optimally set to (0.15×λ)/(NA×T^(0.5)). However, the optimumdistance from the center of the transparent portion to the center lineof the phase shifter is 0.4×λ/NA regardless of the transmittance and thewidth of the phase shifter.

Furthermore, the width d of the phase shifter is preferably not lessthan (0.05×λ)/(NA×T^(0.5)) and not more than (0.2×λ)/(NA×T^(0.5)), andmore preferably not less than (0.1×λ)/(NA×T^(0.5)) and not more than(0.15×λ)/(NA×T^(0.5)).

In this manner, the optimum position of the phase shifter provided asthe auxiliary pattern (i.e., the optimum position of its center line) onthe basis of the outline enhancement method is a position away from thecenter of the transparent portion by a distance with a value not morethan the wavelength λ of the exposing light in this embodiment.Accordingly, differently from the conventional technique where anauxiliary pattern should be provided in a position away from the centerof a transparent portion by a distance with a value not less than thewavelength λ, an auxiliary pattern can be provided also between denselyarranged transparent portions (corresponding to contact patterns) byutilizing the outline enhancement method.

In other words, according to this embodiment, the contrast of the lightintensity distribution between the transparent portion 102 and theauxiliary pattern can be emphasized by utilizing mutual interferencebetween the light passing through the transparent portion 102 and thelight passing through the phase shifter 103, namely, the auxiliarypattern. Also, this effect to emphasize the contrast can be attainedalso in the case where a fine isolated space pattern corresponding tothe transparent portion 102 is formed by, for example, the positiveresist process using the oblique incident exposure. Accordingly, anisolated space pattern and an isolated line pattern or dense patternscan be simultaneously thinned by employing the oblique incidentexposure. Furthermore, even in the case where complicated and fine spacepatterns are close to each other, a pattern with a desired dimension canbe satisfactorily formed.

In this embodiment, the transparent portion 102 is in a square shape ora rectangular shape and the phase shifters 103 each in a rectangularshape (namely, line-shaped patterns) are formed around the transparentportion 102 to be parallel to the respective sides of the transparentportion 102 as shown in FIG. 2A. However, the phase shifter 103 may bein a closed loop shape surrounding the whole transparent portion 102 asshown in FIG. 5A. Also in this case, a distance 2×PW between the centerlines of portions of the phase shifter opposing each other with thetransparent portion 102 sandwiched therebetween (hereinafter, the centerline distance between such portions of a phase shifter is alsodesignated as the shifter center line distance) and the width d of thephase shifter satisfy the aforementioned conditions for attaining thegood pattern formation characteristic.

Also in this embodiment, the transparent portion 102 need not always bein a rectangular shape, but may be, for example, in a polygonal orcircular shape as shown in FIG. 5B or 5C. Furthermore, the phaseshifter(s) 103 surrounding the transparent portion 102 need not alwaysbe in an analogous shape to that of the transparent portion 102 but maybe in any shape as far as the shifter center line distance satisfies theaforementioned condition. Moreover, in the case where a plurality ofphase shifters 103 are individually provided, there is no need toprovide each phase shifter 103 in parallel to each side of thetransparent portion 102 but the phase shifters 103 may be provided, forexample, as shown in FIG. 5C, in any manner as far as they surround thetransparent portion 102 so as to satisfy the aforementioned condition ofthe shifter center line distance. The semi-shielding portion 101 ispreferably sandwiched between the transparent portion 102 and the phaseshifter 103, but the transparent portion 102 may be in contact with thephase shifter 103, for example, as shown in FIG. 5D as far as theshifter center line distance satisfies the aforementioned condition.However, in any of these mask structures described above, the phaseshifter 103 corresponding to the auxiliary pattern is optimally providedso as to have its center line away from the center of the transparentportion 102 by the distance of 0.4×λ/NA, and therefore, the transparentportion 102 preferably used for forming a fine contact pattern is alwayssmaller than a square or a rectangle with a side dimension of 0.8×λ/NA.

Next, the cross-sectional structure of the photomask of this embodimentwill be described. FIGS. 6A through 6D show variations of thecross-sectional structure of the photomask taken along line AB of FIG.2A. Specifically, the photomask having the plane structure composed ofthe transparent portion 102, the semi-shielding portion 101corresponding to a shielding pattern and the phase shifter 103corresponding to the auxiliary pattern has four basic types of thecross-sectional structure as shown in FIGS. 6A through 6D. Now, thebasic types of the cross-sectional structure of FIGS. 6A through 6D willbe described.

First, in the photomask having the cross-sectional structure of the typeshown in FIG. 6A, on a transparent substrate 100 of, for example,quartz, a first phase shift film 104 for causing, in exposing light, aphase difference in the opposite phase (namely, a phase difference notless than (150+360×n) degrees and not more than (210+360×n) degrees(wherein n is an integer)) with respect to the transparent portion 102is formed. Hereinafter, to cause a phase difference in the oppositephase means to cause a phase difference not less than (150+360×n)degrees and not more than (210+360×n) degrees (wherein n is an integer).Furthermore, on the first phase shift film 104, a second phase shiftfilm 105 for causing a phase difference in the opposite phase withrespect to the first phase shift film 104 is formed. The first andsecond phase shift films 104 and 105 have openings in a transparentportion forming region, and the second phase shift film 105 has anopening in a phase shifter forming region. Thus, the semi-shieldingportion 101 composed of a multilayer structure of the second phase shiftfilm 105 and the first phase shift film 104 is formed, and the phaseshifter 103 composed of a single layer structure of the first phaseshift film 104 is formed. Also, an exposed portion of the transparentsubstrate 100 corresponds to the transparent portion 102.

Next, in the photomask having the cross-sectional structure of the typeshown in FIG. 6B, on a transparent substrate 100 of, for example,quartz, a semi-shielding film 106 for causing, in the exposing light, aphase difference in the identical phase (namely, a phase difference notless than (−30+360×n) degrees and not more than (30+360×n) degrees(wherein n is an integer)) with respect to the transparent portion 102is formed. Hereinafter, to cause a phase difference in the identicalphase means to cause a phase difference not less than (−30+360×n)degrees and not more than (30+360×n) degrees (wherein n is an integer).The semi-shielding film 106 has openings respectively in a transparentportion forming region and a phase shifter forming region. Also, aportion in the phase shifter forming region of the transparent substrate100 is trenched by a depth for causing, in the exposing light, a phasedifference in the opposite phase with respect to the transparent portion102. Thus, the phase shifter 103 is formed by the trench portion 100 aof the transparent substrate 100. Specifically, in the photomask of FIG.6B, the semi-shielding film 106 that is formed on the quartz andminimally causes a phase difference with respect to the transparentportion 102 is processed, so that the semi-shielding portion 101 can beformed as a portion where the semi-shielding film 106 is formed, thephase shifter 103 can be formed as the trench portion 100 a of thetransparent substrate 100 where the semi-shielding film 106 has anopening, and the transparent portion 102 can be formed as anotheropening of the semi-shielding film 106 (i.e., an exposed portion of thetransparent-substrate 100).

Next, in the photomask having the cross-sectional structure of the typeshown in FIG. 6C, on a transparent substrate 100 of, for example,quartz, a thin film 107 that minimally changes the phase of the exposinglight on the basis of the transparent portion 102 is formed. In otherwords, the photomask of FIG. 6C is a special one of photomasks belongingto the type of FIG. 6B. Specifically, a metal thin film with a thicknessof, for example, 30 nm or less can be used for forming the thin film 107that causes, with respect to the transparent portion 102, a phasedifference not less than (−30+360×n) degrees and not more than(30+360×n) degrees (wherein n is an integer) and has transmittance of15% or less. The thin film 107 has openings respectively in atransparent portion forming region and a phase shifter forming region.Furthermore, a portion in the phase shifter forming region of thetransparent substrate 100 is trenched by a depth for causing, in theexposing light, a phase difference in the opposite phase with respect tothe transparent portion 102. Thus, similarly to the photomask of FIG.6B, the phase shifter 103 is formed by the trench portion 100 a of thetransparent substrate 100.

In the photomask of the type shown in FIG. 6A or 6B, the phase shiftfilm for causing a phase difference in the opposite phase or thesemi-shielding film for causing a phase difference in the identicalphase should have a thickness approximately several hundreds nm foradjusting the phase. On the contrary, in the photomask of the type ofFIG. 6C, the thin film 107 with a thickness of several tens nm at mostis used, and therefore, refinement processing for patterning in the maskprocess can be easily performed. Examples of the metal material usableas the thin film 107 are metals such as Cr (chromium), Ta (tantalum), Zr(zirconium), Mo (molybdenum) and Ti (titanium), and alloy of any ofthese metals. Specific examples of the alloy are Ta—Cr alloy, Zr—Sialloy, Mo—Si alloy and Ti—Si alloy. When the photomask of the type ofFIG. 6C is employed, since the film to be processed is the thin film107, the refinement processing in the mask process can be easilyperformed. Therefore, in the case where it is necessary to provide avery fine pattern between the transparent portion 102 and the phaseshifter 103 for realizing the outline enhancement method, the photomaskof the type shown in FIG. 6C has a very good mask structure.

Ultimately, in the photomask with the cross-sectional structure of thetype shown in FIG. 6D, on a transparent substrate 100 of, for example,quartz, a phase shift film 108 for causing, in the exposing light, aphase difference in the opposite phase with respect to the phase shifter103 is formed. The phase shift film 108 has openings respectively in atransparent portion forming region and a phase shifter forming region.Furthermore, in order to accord the phase of light passing through thetransparent portion 102 with the phase of light passing through thesemi-shielding portion 101, a portion in the transparent portion formingregion of the transparent substrate 100 is trenched by a depth forcausing a phase difference in the opposite phase with respect to thephase shifter 103. Specifically, in the photomask of FIG. 6D, the quartzcorresponding to the transparent substrate 100 and the phase shift film108 for causing a phase difference in the opposite phase arerespectively processed, so that the semi-shielding portion 101 can beformed as the portion where the phase shift film 108 is formed, thetransparent portion 102 can be formed as the trench portion 100 a of thetransparent substrate 100 where the phase shifter film 108 has anopening, and the phase shifter 103 can be formed as an opening of thephase shift film 108 (i.e., an exposed portion of the transparentsubstrate 100). In the photomask of FIG. 6D, the phase shifter 103 thatis formed as a fine pattern on the mask is formed as a simple opening ofthe phase shift film 108, and the transparent portion 102 correspondingto a comparatively large opening is an etched portion of the quartz.Therefore, the depth of the etched portion of the quartz can be easilycontrolled. Accordingly, the photomask of the type of FIG. 6C has aparticularly good mask structure for realizing the outline enhancementmethod.

It is noted that although each of the semi-shielding film, the phaseshift film and the like is shown as a single-layered film in FIGS. 6Athrough 6D, it goes without saying that each film may be formed as amultilayer film.

Modification of Embodiment 1

A photomask according to a modification of Embodiment 1 will now bedescribed with reference to the accompanying drawings.

FIG. 7A is a plan view of the photomask of this modification. Thephotomask of this modification is used for forming a fine space pattern.Specifically, a desired pattern to be formed in this modification is aline-shaped fine space pattern differently from Embodiment 1 in which adesired pattern is a contact hole pattern. Herein, a line-shaped patternmeans a pattern having an optically sufficiently large longitudinaldimension and more specifically means a pattern with a longitudinaldimension of 2×λ/NA or more.

As shown in FIG. 7A, on a transparent substrate 100, a semi-shieldingportion 101 is formed so as to cover a sufficiently large area in thesame manner as in the photomask of Embodiment 1 shown in FIG. 2A. Also,in a position in the semi-shielding portion 101 corresponding to adesired space pattern to be formed on a wafer through the exposure, anopening pattern corresponding to a transparent portion 102 is provided.Furthermore, auxiliary patterns corresponding to phase shifters 103 areprovided around the transparent portion 102 with the semi-shieldingportion 101 sandwiched therebetween, for example, so as to be parallelto the respective long sides of the line-shaped transparent portion 102.In other words, the phase shifters 103 are provided so as to sandwichthe transparent portion 102. It is assumed in this modification that thesemi-shielding portion 101 has transmittance of, for example, 6%.Specifically, in forming a line-shaped space pattern, the quantity oflight passing through the transparent portion 102 is larger than informing a contact hole pattern, and therefore, the preferabletransmittance of the semi-shielding portion 101 is lower than in forminga contact hole pattern, and thus, the preferable transmittance isapproximately 6%.

Assuming that the exposure wavelength and the numerical aperture of anoptical system using the photomask of FIG. 7A are λ and NA,respectively, the most preferable structure for forming a fine spacepattern is a structure in which a distance between the center lines ofthe phase shifters 103 paring and opposing each other with thetransparent portion 102 sandwiched therebetween is 0.65×λ/NA asdescribed below. In other words, each phase shifter 103 is optimallyprovided so as to have its center line in a position away from thecenter of the transparent portion 102 by a distance of 0.325×λ/NA.Furthermore, in the case where the transmittance of the phase shifter103 is set to be the same as that of the transparent portion 102, thewidth of the phase shifter 103 is optimally set to 0.10×λ/NA.

Now, a good pattern formation characteristic of the photomask with theaforementioned structure exhibited in forming a fine space pattern, andmore particularly, in forming a line-shaped space pattern with a widthof 0.4×λ/NA or less will be described on the basis of a result ofsimulation.

It is assumed in the simulation that the transparent portion 102 is aline-shaped pattern having a width W, that each phase shifter 103provided in parallel to each long side of the transparent portion 102 isa rectangular pattern (a line-shaped pattern) with a width d and thatthe center line of each phase shifter 103 is disposed in a position awayfrom the center of the transparent portion 102 by a distance PW in thephotomask of FIG. 7A. In other words, a distance between the centerlines of a pair of phase shifters 103 opposing each other with thetransparent portion 102 sandwiched therebetween is 2×PW. Also, it isassumed that the semi-shielding portion 101 working as the backgroundhas transmittance of 6%. Under these conditions, the light intensity issimulated with respect to various combinations of the width W, thedistance PW and the width d. In this simulation, optical calculation iscarried out on the assumption that the exposure is carried out with theexposure wavelength λ of 193 nm and the numerical aperture NA of 0.7.Furthermore, ⅔ annular illumination having the outer diameter with adegree of coherence of 0.8 and the inner diameter with a degree ofcoherence of 0.53 is assumed to be used.

FIG. 7B shows a light intensity distribution formed on a wafer (in aposition corresponding to line AB of FIG. 7A) through the exposure usingthe photomask of FIG. 7A. The light intensity distribution of FIG. 7Bhas a profile with a peak in a position corresponding to the center ofthe transparent portion 102. In this case, it is necessary for the peakintensity Io to be not less than a given value in order to sensitize aresist corresponding to the center of the transparent portion 102. Thepeak intensity Io necessary for sensitizing the resist depends upon theused resist material, and it has been experimentally found that the peakintensity Io necessary for forming a fine space pattern with a width of0.4×λ/NA or less is approximately 0.25.

Results of analysis of the photomask of this modification performedsimilarly to obtain the results shown in FIGS. 3A through 3C inEmbodiment 1 are shown in FIGS. 8A through 8C.

FIG. 8A shows the combinations of the width W, the distance PW and thewidth d for attaining the peak intensity Io of 0.25 in the photomask ofFIG. 7A obtained as a result of the simulation. Specifically, FIG. 8Ashows the width W of the transparent portion 102 for attaining the peakintensity Io of 0.25 plotted against the shifter center line distance2×PW. Also, FIG. 8A shows the relationships between the shifter centerline distance 2×PW and the width W obtained when the width d of thephase shifter 103 is 20 nm, 30 nm, 40 nm and 50 nm. In other words, thelight intensity distribution having the peak intensity Io of 0.25 can beformed by employing any of all the combinations of the distance PW, thewidth W and the width d shown in the graph of FIG. 8A. Furthermore,among these combinations, one having the maximum depth of focus or themaximum exposure margin corresponds to a mask structure having a goodpattern formation characteristic.

FIG. 8B shows a result of simulation for the depth of focus in which aspace pattern with a width of 100 nm is formed by using a mask patternhaving the combination of the distance PW, the width W and the width dshown in the graph of FIG. 8A. In FIG. 8B, the abscissa indicates theshifter center line distance 2×PW and the value of the depth of focus isplotted by using the width d as a parameter on the ordinate.

Similarly, FIG. 8C shows a result of simulation for the exposure marginin which a space pattern with a width of 100 nm is formed by using amask pattern having the combination of the distance PW, the width W andthe width d shown in the graph of FIG. 8A. In FIG. 8C, the abscissaindicates the shifter center line distance 2×PW and the value of theexposure margin is plotted by using the width d as a parameter on theordinate.

As shown in FIGS. 8B and 8C, regardless of the value of the width d ofthe phase shifter, both the depth of focus and the exposure margin havethe maximum values when the shifter center line distance 2×PW has avalue in the vicinity of 0.65×λ/NA (=approximately 180 nm). That theoptimum value of the shifter center line distance 2×PW does not dependupon the width d of the phase shifter means that the optimum value doesnot depend upon the transmittance of the phase shifter, either.

Furthermore, in phase shifters having the center line distance 2×PW ofapproximately 0.65×λ/NA, both the depth of focus and the exposure marginhave sufficiently large values when the width d of the phase shifter isapproximately 0.10×λ/NA (=30 nm).

It is understood from these results that a mask structure in which thephase shifters 103 are provided to be paired each other with thetransparent portion 102 sandwiched therebetween, each phase shifter 103has a width of 0.10×λ/NA and the shifter center line distance is0.65×λ/NA is good for forming a fine space pattern. As compared withEmbodiment 1, since the transparent portion 102 is in the shape of aline in this modification, the light interference effect is large, andhence, the optimum position of each phase shifter 103 is closer to thecenter of the transparent portion 102.

Furthermore, referring to the graphs of FIGS. 8B and 8C in detail, it isunderstood that a large depth of focus and a large exposure margin canbe attained as far as the width d of the phase shifter is not less than0.05×λ/NA and not more than 0.2×λ/NA similarly to Embodiment 1. Also, itis understood that a large depth of focus and a large exposure margincan be attained as far as the shifter center line distance is not lessthan 0.5×λ/NA and not more than 0.9×λ/NA (namely, the distance betweenthe center line of the phase shifter and the center of the transparentportion is not less than 0.25×λ/NA and not more than 0.45×λ/NA).Furthermore, in order to attain a depth of focus and an exposure marginapproximate to their maximum values, the width of the phase shifter ispreferably not less than 0.1×λ/NA and not more than 0.15×λ/NA, and theshifter center line distance is preferably not less than 0.55×λ/NA andnot more than 0.85×λ/NA (namely, the distance between the center line ofthe phase shifter and the center of the transparent portion ispreferably not less than 0.275×λ/NA and not more than 0.425×λ/NA).

The results shown in FIGS. 8B and 8C are described as data obtained inthe exemplified case where the numerical aperture NA is 0.7, andsimulation is similarly performed on the assumption that the numericalaperture NA is 0.6 and 0.8. As a result, it is confirmed that theoptimum mask structure does not depend upon the value of the numericalaperture NA.

In this modification, the optimum value of the width d of the phaseshifter is 0.10×λ/NA on the assumption that the transmittance of thephase shifter is the same as that of the transparent portion. In thecase where the phase shifter has transmittance different from that ofthe transparent portion, namely, in the case where the effectiverelative transmittance of the phase shifter (the auxiliary pattern) tothe transparent portion is not 1, the width of the phase shifter ischanged in accordance with the relative transmittance for realizing anequivalent transmitting property. Specifically, assuming that therelative transmittance is T, the width d of the phase shifter ispreferably set to (0.10×λ)/(NA×T^(0.5)). However, the optimum distancefrom the center of the transparent portion to the center line of thephase shifter is 0.325×λ/NA regardless of the transmittance and thewidth of the phase shifter.

Furthermore, the width d of the phase shifter is preferably not lessthan (0.05×λ)/(NA×T^(0.5)) and not more than (0.2×λ)/(NA×T^(0.5)), andmore preferably not less than (0.1×λ)/(NA×T^(0.5)) and not more than(0.15×λ)/(NA×T^(0.5)).

In this manner, the optimum position of the phase shifter provided asthe auxiliary pattern on the basis of the outline enhancement method(i.e., the optimum position of its center line) is a position away fromthe center of the transparent portion by a distance with a value notmore than the wavelength λ of the exposing light in this embodiment.Accordingly, differently from the conventional technique where anauxiliary pattern should be provided in a position away from the centerof a transparent portion by a distance with a value not less than thewavelength λ an auxiliary pattern can be provided between denselyarranged transparent portions (corresponding to space patterns) byutilizing the outline enhancement method.

In other words, according to this modification, the contrast of thelight intensity distribution between the transparent portion 102 and theauxiliary pattern can be emphasized by utilizing mutual interferencebetween the light passing through the transparent portion 102 and thelight passing through the phase shifter 103, namely, the auxiliarypattern. Also, this effect to emphasize the contrast can be attainedalso in the case where a fine isolated space pattern corresponding tothe transparent portion 102 is formed by, for example, the positiveresist process using the oblique incident exposure. Accordingly, anisolated space pattern and an isolated line pattern or dense patternscan be simultaneously thinned by employing the oblique incidentexposure. Furthermore, even in the case where complicated and fine spacepatterns are close to each other, a pattern with a desired dimension canbe satisfactorily formed.

In this modification, the phase shifters 103 are provided in parallel tothe transparent portion 102. However, the phase shifters 103 need not becompletely parallel to the transparent portion 102. Specifically, evenwhen a desired pattern is, for example, a simple rectangular pattern,the pattern width of a transparent portion for obtaining the desiredpattern is sometimes changed on a photomask with respect to each smalllength unit. In such a case, there is no need to provide the phaseshifters so as to completely follow the change of the outline of thetransparent portion. In other words, the phase shifters 103 may beprovided substantially parallel to the transparent portion 102. However,the optimum value of the shifter center line distance, namely, thedistance between the center lines of the phase shifters 103 pairing witheach other with the transparent portion 102 sandwiched therebetween, is0.65×λ/NA, and therefore, the transparent portion 102 preferably usedfor forming a fine space pattern is always a line pattern with a widthsmaller than 0.65×λ/NA.

EMBODIMENT 2

A photomask according to Embodiment 2 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 9 is a plan view of the photomask of Embodiment 2. The photomask ofthis embodiment is used for simultaneously forming a plurality of finecontact patterns.

As shown in FIG. 9, on a transparent substrate 200, a semi-shieldingportion 201 is formed so as to cover a sufficiently large area. Also, inpositions in the semi-shielding portion 201 corresponding to desiredcontact patterns to be formed on a wafer through the exposure, atransparent portion 202, a pair of transparent portions 203 and 204 anda pair of transparent portions 205 and 206 are provided as openingpatterns. In this case, the transparent portion 202 is an openingpattern corresponding to an isolated contact pattern, and each of thetransparent portions 203 and 205 is an opening pattern corresponding toa contact pattern having another contact pattern closely disposed.Furthermore, around the transparent portion 202, auxiliary patternscorresponding to phase shifters 207 are provided with the semi-shieldingportion 201 sandwiched therebetween, for example, so as to be parallelto respective sides of the transparent portion 202 in the shape of asquare or a rectangle and to surround the transparent portion 202.Similarly, around each of the transparent portions 203 through 206,auxiliary patterns corresponding to phase shifters 208, 209, 210 or 211are provided with the semi-shielding portion 201 sandwichedtherebetween, for example, so as to be parallel to respective sides ofeach of the transparent portions 203 through 206 and to surround thetransparent portion 203, 204, 205 or 206.

The phase shifters 207 provided around the transparent portion 202 aredisposed so as to attain a mask structure good for forming an isolatedcontact pattern, and each phase shifter 207 has a width d0.

The transparent portion 203 is close to the different transparentportion 204. In this case, among the phase shifters 208 and 209respectively provided around the transparent portions 203 and 204, thoseprovided in an area sandwiched between the transparent portions 203 and204 are referred to as a phase shifter 208 a and a phase shifter 209 a.Furthermore, the transparent portion 205 is close to the differenttransparent portion 206. In this case, among the phase shifters 210 and211 respectively provided around the transparent portions 205 and 206,those provided in an area sandwiched between the transparent portions205 and 206 are referred to as a phase shifter 210 a and a phase shifter211 a.

As a characteristic of this embodiment, assuming that the phase shifters208 a and 209 a respectively have widths d1 and d2 and that a distancebetween the center lines of the phase shifters 208 a and 209 a is G1,the photomask has a structure in which a relationship (d1+d2)<2×d0 issatisfied under a condition of the distance G1 being 0.5×λ/NA or less.In other words, when d1=d2, d1<d0 and d2<d0. In this case, among thephase shifters 208 surrounding the transparent portion 203, each ofphase shifters 208 b provided on sides not close to the differenttransparent portion 204 has the width d0.

Furthermore, as another characteristic of this embodiment, assuming thatthe phase shifters 210 a and 211 a respectively have widths d3 and d4and that a distance between the center lines of the phase shifters 210 aand 211 a is G2, the photomask has a structure in which a relationship(d3+d4)<(d1+d2)<2×d0 is satisfied under a condition of G2<G1<0.5×λ/NA.In other words, when d3=d4 and d1=d2, d3=d4<d1=d2<d0. In this case,among the phase shifters 210 surrounding the transparent portion 205,each of phase shifters 210 b provided on sides not close to thedifferent transparent portion 206 has the width d0.

Specifically, in this embodiment, in the relationship between phaseshifters surrounding one transparent portion and phase shifterssurrounding another transparent portion, in the case where any phaseshifters of these transparent portions are adjacent and close to eachother and spaced by a given or smaller distance, these close phaseshifters have smaller widths than the other phase shifters having noadjacent and close phase shifter spaced by the given or smallerdistance. In this case, the widths of the phase shifters adjacent andclose to each other and spaced by the given or smaller distance arepreferably in proportion to a distance (a close distance) between thesephase shifters. Alternatively, in the case of the photomask of FIG. 9, adifference between the width d1 of the phase shifter 208 a (or the widthd2 of the phase shifter 209 a) and the width d3 of the phase shifter 210a (or the width d4 of the phase shifter 211 a) is preferably inproportion to a difference between the distances G1 and G2.

According to this embodiment, the contrast of the light intensitydistribution between the transparent portion and the auxiliary patterncan be emphasized by utilizing mutual interference between light passingthrough each transparent portion and light passing through the phaseshifters, namely, the auxiliary patterns, provided around thetransparent portion. Also, this effect to emphasize the contrast can beattained also in the case where a fine isolated space patterncorresponding to the transparent portion is formed by, for example, thepositive resist process using the oblique incident exposure.Accordingly, an isolated space pattern and an isolated line pattern ordense patterns can be simultaneously thinned by employing the obliqueincident exposure. Furthermore, even in the case where complicated andfine space patterns are close to each other, a pattern with a desireddimension can be satisfactorily formed.

Now, an isolated contact hole and densely arranged contact holessatisfactorily formed by using the photomask of this embodiment will bedescribed in detail on the basis of results of simulation.

FIG. 10A is a plan view of a photomask used in the simulation forconfirming the effect of this embodiment. As shown in FIG. 10A, on atransparent substrate 250, a semi-shielding portion 251 is formed so asto cover a sufficiently large area. Also, in positions in thesemi-shielding portion 251 corresponding to desired contact patterns tobe formed on a wafer through the exposure, a plurality of transparentportions 252 each in the shape of a square with a side dimension W areprovided to be adjacent to one another. Also, around each of thetransparent portions 252, phase shifters (auxiliary patterns) 253 areprovided so as to have their center lines in positions away from thecenter of each transparent portion 252 by a distance PW0. In this case,each phase shifter 253 is in a rectangular shape with a width d and alength t. Furthermore, a distance between the center lines of the phaseshifters 253 adjacent and close to each other in an area sandwichedbetween the adjacent transparent portions 252 (hereinafter referred toas the adjacent shifter distance) is assumed to be a distance G.

FIG. 10B shows the profile of a light intensity distribution formedthrough the exposure using the photomask of FIG. 10A. In FIG. 10B, thelight intensity obtained at the center of the transparent portion 252 isexpressed as Ip, the light intensity obtained at the center between theadjacent transparent portions 252 is expressed as Is, and the lightintensity obtained in a position where the light intensity is minimum inthe periphery of the transparent portion 252 is expressed as Ib. In thiscase, the center between the adjacent transparent portions 252corresponds to the center of the adjacent phase shifters 253. Also, thelight intensity simulation is performed under conditions of the exposurewavelength λ of 193 nm and the numerical aperture NA of 0.65.Furthermore, ⅔ annular illumination having the outer diameter with adegree of coherence of 0.8 and the inner diameter with a degree ofcoherence of 0.53 is assumed to be used. In addition, the transmittanceof the semi-shielding portion 201 is set to 6%.

Furthermore, in the photomask of FIG. 10A, in order that each contactpattern can be satisfactorily formed even in an isolated state, thewidth d of each phase shifter 253 is set to approximately 0.15×λ/NA(=approximately 44 nm) and the distance PW0 between the phase shifter253 and the transparent portion 252 is set to approximately 0.4×λ/NA(=approximately 120 nm). Moreover, in order to adjust the contact holesize to a desired size of 100 nm, the side dimension W of thetransparent portion 252 and the length t of the phase shifter 253 areset to 160 nm. In the aforementioned mask structure for satisfactorilyforming an isolated pattern, dependency of the light intensities Ib andIs on the adjacent shifter distance G calculated through the simulationis shown in a graph of FIG. 11A, wherein the value of the adjacentshifter distance G is normalized by λ/NA.

As shown in FIG. 11A, when the adjacent shifter distance G is largerthan 0.5×λ/NA, the light intensity Ib is sufficiently low. In otherwords, a light intensity distribution with high contrast is realized inthis case, and therefore, good pattern formation can be realized byusing the photomask. However, when the adjacent shifter distance G isnot more than 0.5×λ/NA, the light intensity Ib is large. In other words,the contrast is lowered because a sufficient shielding property cannotbe attained between the adjacent two contact patterns in the contactpattern formation. In this case, good pattern formation cannot beperformed.

This phenomenon occurs for the following reason: When a distance betweencontact holes is small in desired dense contact holes, the width of asemi-shielding portion sandwiched between phase shifters on the mask isso small that the semi-shielding portion cannot transmit sufficientlight. Now, this phenomenon will be described in more detail.

An opening pattern (a transparent portion) and a semi-shielding portionare regions for transmitting light in the positive phase while a phaseshifter is a region for transmitting light in the negative phase. Also,the light intensity Ib in a dark part (in the periphery of thetransparent portion) is obtained by canceling the light in the positivephase having passed through the opening pattern and the semi-shieldingportion by the light in the negative phase having passed through thephase shifter. The light intensity Ib in the dark part can besufficiently small when the light in the positive phase is balanced withthe light in the negative phase. Specifically, when the adjacent shifterdistance G is sufficiently large, the quantity of light passing throughthe semi-shielding portion is sufficiently large, and hence, the lightintensity Is corresponds to the transmittance of the semi-shieldingportion. However, when the adjacent shifter distance G is λ/NA or less,the area of the semi-shielding portion sandwiched between the phaseshifters is accordingly reduced, and hence, the quantity of the lightpassing through the semi-shielding portion is reduced. This can be foundalso based on the value of the light intensity Is being reduced when theadjacent shifter distance G is λ/NA or less in the graph of FIG. 11A. Inother words, in the relationship between the light in the positive phaseand the light in the negative phase, which are balanced when thesemi-shielding portion with a sufficiently large area is sandwichedbetween the adjacent phase shifters, the light in the negative phasebecomes excessive when the area of the semi-shielding portion isreduced. As the light in the negative phase becomes more excessive, thelight intensity Ib is also increased, resulting in lowering the contrastin the light intensity distribution.

Accordingly, in order to avoid this phenomenon, the quantity of thelight passing through the phase shifter is reduced as the area of thesemi-shielding portion sandwiched between the adjacent phase shifters isreduced. As one method employed for this purpose, the width of the phaseshifter is reduced.

The present inventor has found the following through detailed analysisof the simulation result: Assuming that a phase shifter capable ofrealizing good pattern formation when the adjacent shifter distance G issufficiently large has a width d0, when the adjacent shifter distance Gis 0.5×λ/NA or less, dense contact hole patterns can be alsosatisfactorily formed by setting the width d of the phase shifter tod0×(0.5+G)/(λ/NA).

FIG. 11B shows the result of simulation similar to that performed forobtaining FIG. 10B, and specifically shows the light intensitydistribution formed in a position corresponding to line AB of thephotomask of FIG. 10A. FIG. 11B shows the results of the light intensitydistribution simulation performed by assuming that the adjacent shifterdistance G is 0.3×λ/NA with the width d set to the width d0(approximately 0.15×λ/NA (=approximately 44 nm)) that is an optimumdimension for forming an isolated contact pattern and with the width dof the phase shifter reduced to 0.8×d0. As shown in FIG. 11B, a lightintensity distribution with high contrast can be obtained by reducingthe width d of the phase shifter.

Also, FIG. 11C shows the result of the simulation similar to thatperformed for obtaining FIG. 10B, and specifically shows the lightintensity distribution formed in the position corresponding to line ABin the photomask of FIG. 10A. FIG. 11C shows the results of the lightintensity distribution simulation performed by assuming that theadjacent shifter distance G is further reduced to 0.2×λ/NA with thewidth d of the phase shifter set to the width d0 and with the width dreduced to 0.7×d0. As shown in FIG. 11C, a photomask capable ofrealizing a light intensity distribution with high contrast can beobtained by reducing the width d of the phase shifter in accordance withthe reduction of the adjacent shifter distance G.

On the basis of the results of these simulations, it can be understoodthat when phase shifters (auxiliary patterns) are arranged on the basisof the outline enhancement method, if phase shifters respectivelycorresponding to adjacent transparent portions are provided in parallelto each other with a semi-shielding portion sandwiched therebetween andwith the adjacent shifter distance set to 0.5×λ/NA or less, the width ofeach phase shifter is preferably reduced in proportion to the adjacentshifter distance.

As shown in FIG. 12A, a typical distance (an optimum distance) PW0between the center of an opening (i.e., a transparent portion 252) tothe center line of a phase shifter 253 for forming a fine contactpattern is 0.4×λ/NA (see Embodiment 1). Accordingly, the case where theadjacent shifter distance G is 0.5×λ/NA or less, namely, the case wherethe width d of a phase shifter 253 disposed between the adjacenttransparent portions is preferably reduced, corresponds to the case offorming dense holes in which a desired distance P (=2×PW0+G) between thecenters of the transparent portions 252 corresponding to adjacentcontact holes is 1.3×λ/NA or less as shown in FIG. 12B.

Accordingly, in such a mask structure, assuming that a phase shifter 253provided in an area sandwiched between the transparent portions 252(opening patterns) adjacent to each other with the distance P betweentheir centers of 1.3×λ/NA or less has a width d and that another phaseshifter 253 provided in the other area (i.e., an area where the distanceP is not 1.3×λ/NA or less) has a width d0 as shown in FIG. 13A, thesewidths d and d0 are set to satisfy d<d0, whereas each phase shifter 253has a length t regardless of its position.

In FIG. 13A, the width of the phase shifter 253 provided in the areasandwiched between the adjacent transparent portions (opening patterns)252 is reduced in order to reduce the quantity of the light in thenegative phase passing through the phase shifter 253. Accordingly, withrespect to the phase shifter 253 provided between the adjacent openingpatterns, the two phase shifters 253 shown in FIG. 13A may be replacedwith one phase shifter 253 shown in FIG. 13B as far as its width d1satisfies d1<2×d0.

Also, in FIG. 13A, the width of the phase shifter 253 sandwiched betweenthe adjacent opening patterns is reduced. Instead, the length of thephase shifter 253 may be reduced as shown in FIG. 13C. Specifically,assuming that the two phase shifters 253 provided between the openingpatterns have a width d2 and a length t2, the width and the length areset to satisfy t2×d2<t×d0.

Furthermore, a mask structure as shown in FIG. 14A may be employed.Specifically, the phase shifters 253 sandwiched between the adjacentopening patterns is combined to one phase shifter, and assuming thatthis one phase shifter 253 has a width d3 and a length t3, the area ofthe phase shifter 253, namely, d3×t3, is set to be smaller than 2×t×d0.

Moreover, a mask structure as shown in FIG. 14B may be employed.Specifically, as far as the area of the phase shifter 253 providedbetween the adjacent opening patterns is smaller than 2×t×d0, the phaseshifter 253 may be in an arbitrary shape. In FIG. 14B, two rectangularpatterns working as the phase shifter 253 provided between the adjacentopening patterns are arranged so as to extend along a direction alongwhich the opening patterns (transparent portions) 252 are aligned. Inthis case, assuming that each phase shifter 253 has a width d4 and alength t4, the width and the length are set to satisfy t4×d4<t×d0.Although the two rectangular patterns are arranged as the phase shifters253 in FIG. 14B, three, four or more rectangular patterns may bearranged instead as far as the total area of the phase shifters 253provided between the adjacent opening patterns is smaller than 2×d0×t.Furthermore, in each of FIGS. 13B, 14A and 14B, when the area (the totalarea in FIG. 14B) of the phase shifter(s) 253 provided between theadjacent opening patterns is halved correspondingly to the pair ofadjacent transparent portions 252, the halved area is smaller than thearea, t×d0, of the other phase shifter 253 provided in the area otherthan that between the opening patterns.

As described so far, according to this embodiment, in the case wheredense contact patterns are formed, phase shifters provided betweentransparent portions corresponding to dense contact holes are deformedso as to reduce the quantity of light in the opposite phase passingthrough these phase shifters. As a result, a photomask capable of goodpattern formation can be realized.

Also in this embodiment, the cross-sectional structure of the photomaskmay be, for example, any of the cross-sectional structures shown inFIGS. 6A through 6D described in Embodiment 1.

Modification of Embodiment 2

A photomask according to a modification of Embodiment 2 of the inventionwill now be described with reference to the accompanying drawings.

FIG. 15 is a plan view of the photomask of this modification. Thephotomask of this modification is used for simultaneously forming aplurality of fine line-shaped space patterns. Specifically, desiredpatterns to be formed in this modification are fine line-shaped spacepatterns differently from Embodiment 2 where the desired patterns arethe contact hole patterns.

As shown in FIG. 15, on a transparent substrate 270, a semi-shieldingportion 271 is formed so as to cover a sufficiently large area. Also, atransparent portion 272, a pair of transparent portions 273 and 274 anda pair of transparent portions 275 and 276 are provided in positions inthe semi-shielding portion 201 corresponding to the desired spacepatterns to be formed on a wafer through the exposure. In this case, thetransparent portion 272 is an opening pattern corresponding to anisolated space pattern, and each of the transparent portions 273 and 275is an opening pattern corresponding to a space pattern having anotherspace pattern closely disposed. Furthermore, auxiliary patternscorresponding to phase shifters 277 are provided around the transparentportion 272 with the semi-shielding portion 271 sandwiched therebetweenso as to be parallel to the respective long sides of the line-shapedtransparent portion 272. Similarly, auxiliary patterns corresponding tophase shifters 278 through 281 are provided respectively around thetransparent portions 273 through 276 with the semi-shielding portion 271sandwiched therebetween so as to be parallel to the respective longsides of the line-shaped transparent portions 273 through 276.

The phase shifters 277 provided around the transparent portion 272 arearranged so as to attain a mask structure good for forming an isolatedfine space pattern, and each phase shifter 277 has a width d0.

The transparent portion 273 is close to the different transparentportion 274. In this case, among the phase shifters 278 and 279respectively provided around the transparent portions 273 and 274, thoseprovided in an area sandwiched between the transparent portions 273 and274 are referred to as a phase shifter 278 a and a phase shifter 279 a.Furthermore, the transparent portion 275 is close to the differenttransparent portion 276. In this case, among the phase shifters 280 and281 respectively provided around the transparent portions 275 and 276,those provided in an area sandwiched between the transparent portions275 and 276 are referred to as a phase shifter 280 a and a phase shifter281 a.

As a characteristic of this embodiment, assuming that the phase shifters278 a and 279 a respectively have widths d1 and d2 and that a distancebetween the center lines of the phase shifters 278 a and 279 a is G1,the photomask has a structure in which a relationship (d1+d2)<2×d0 issatisfied under a condition of the distance G1 being 0.5×λ/NA or less asin Embodiment 2. In other words, when d1=d2, d1<d0 and d2<d0. In thiscase, among the phase shifters 278 surrounding the transparent portion273, each of phase shifters 278 b provided on sides not close to thedifferent transparent portion 274 has the width d0 as in Embodiment 2.

Furthermore, as another characteristic of this embodiment, assuming thatthe phase shifters 280 a and 281 a respectively have widths d3 and d4and that a distance between the center lines of the phase shifters 280 aand 281 a is G2, the photomask has a structure in which a relationship(d3+d4)<(d1+d2)<2×d0 is satisfied under a condition of G2<G1<0.5×λ/NA asin Embodiment 2. In other words, when d3=d4 and d1=d2, d3=d4<d1=d2<d0.In this case, among the phase shifters 280 surrounding the transparentportion 275, each of phase shifters 280 b provided on sides not close tothe different transparent portion 276 has the width d0.

Specifically, in this modification, similarly to Embodiment 2, in therelationship between phase shifters surrounding one transparent portionand phase shifters surrounding another transparent portion, in the casewhere any phase shifters of these transparent portions are adjacent andclose to each other and spaced by a given or smaller distance, thesephase shifters have smaller widths than the other phase shifters havingno adjacent and close phase shifter spaced by the given or smallerdistance. In this case, the widths of the phase shifters adjacent andclose to each other and spaced by the given or smaller distance arepreferably in proportion to a distance (a close distance) between thesephase shifters. Alternatively, in the case of the photomask of FIG. 15,a difference between the width d1 of the phase shifter 278 a (or thewidth d2 of the phase shifter 279 a) and the width d3 of the phaseshifter 280 a (or the width d4 of the phase shifter 281 a) is preferablyin proportion to a difference between the distances G1 and G2.

According to this modification, similarly to Embodiment 2, the contrastof the light intensity distribution between the transparent portion andthe auxiliary pattern can be emphasized by utilizing mutual interferencebetween light passing through each transparent portion and light passingthrough the phase shifters, namely, the auxiliary patterns, providedaround the transparent portion. Also, this effect to emphasize thecontrast can be attained also in the case where a fine isolated spacepattern corresponding to the transparent portion is formed by, forexample, the positive resist process using the oblique incidentexposure. Accordingly, an isolated space pattern and an isolated linepattern or dense patterns can be simultaneously thinned by employing theoblique incident exposure. Furthermore, even in the case wherecomplicated and fine space patterns are close to each other, a patternwith a desired dimension can be satisfactorily formed.

Accordingly, also in this modification, in the case where a pair ofphase shifters are provided to be close to each other and to besandwiched between adjacent opening patterns (transparent portions) andthe adjacent shifter distance G therebetween is smaller than 0.5×λ/NA, aphotomask capable of forming a light intensity distribution with highcontrast even in forming dense space patterns can be realized byreducing the width of the phase shifters in proportion to the adjacentshifter distance G in the same manner as in Embodiment 2.

In the above description, the respective line-shaped transparentportions are independent patterns. However, the mask structure of thismodification can be used even when the line-shaped transparent portionsare not independent patterns as far as the above-described structure isemployed in a specified area. In other words, the respective transparentportions may be connected to one another to form one pattern in areasother than the specified area.

A typical distance (an optimum distance) PW0 between the center of anopening pattern and the center line of a phase shifter for forming afine space pattern is 0.325×λ/NA (see the modification of Embodiment 1).Accordingly, the case where the adjacent shifter distance G is 0.5×λ/NAor less, namely, the case where the width d of a phase shifter disposedbetween the adjacent transparent portions is preferably reduced,corresponds to the case of dense holes in which a desired distance P(=2×PW0+G) between the transparent portions corresponding to adjacentspace patterns is 1.15×λ/NA or less.

Accordingly, in such a mask structure, assuming that a phase shifter 293provided in an area sandwiched between transparent portions 292 (openingpatterns) adjacent to each other with the distance P between theircenters of 1.15×λ/NA or less has a width d and that another phaseshifter 293 provided in the other area (i.e., an area where the distanceP is not 1.15×λ/NA or less) has a width d0 as shown in FIG. 16A, thesewidths d and d0 are set to satisfy d<d0.

In FIG. 16A, the width of the phase shifter 293 provided in the areasandwiched between the adjacent transparent portions (opening patterns)292 is reduced in order to reduce the quantity of the light in thenegative phase passing through the phase shifter 293. Accordingly, withrespect to the phase shifters 293 provided between the adjacent openingpatterns, the two phase shifters 293 shown in FIG. 16A may be replacedwith one phase shifter 293 shown in FIG. 16B as far as its width d1satisfies d1<2×d0.

Also, in FIG. 16A, the width of the phase shifter 293 sandwiched betweenthe adjacent opening patterns is reduced. Alternatively, the phaseshifter 293 sandwiched between the adjacent opening patterns may bedivided into a plurality of patterns as shown in FIG. 16C, so as toreduce the area of the phase shifter 293 (that is, the area per unitlength along an extending direction of the opening pattern correspondingto the transparent portion 292). Specifically, assuming that the phaseshifter 293 sandwiched between the adjacent opening patterns is dividedinto a plurality of patterns each with a width d2 and a length t andthat these plural patterns are arranged along the extending direction ofthe opening patterns at a cycle TT, d2×t/TT is set to be smaller than2×d0, whereas TT is preferably (λ/NA)/2 or less. This is for thefollowing reason: In the case where the phase shifter 293 is divided atthe cycle TT not more than the resolution limit ((λ/NA)/2) of theexposure system, the quantity of light passing through the phase shifter293 is reduced in proportion to the area reduction of the phase shifter293 but the divided shape of the phase shifter 293 does not affect theshape of the light intensity distribution.

In each of FIGS. 16A through 16C, a semi-shielding portion 291 is formedon a transparent substrate 290 so as to cover a sufficiently large area,and the pair of line-shaped transparent portions 292 are provided to beadjacent to each other in the semi-shielding portion 291 in positionscorresponding to desired space patterns to be formed on a wafer throughthe exposure.

Furthermore, in each of FIGS. 16B and 16C, when the area of the phaseshifters 293 (the total area in FIG. 16C) provided between the openingpatterns is halved correspondingly to the pair of transparent portions292, the halved area is smaller than the area (the area per unit lengthalong the extending direction of the opening patterns corresponding tothe transparent portions 292) of the phase shifter 293 provided in thearea other than that between the opening patterns.

As described so far, according to this modification, in forming densespace patterns, a phase shifter provided between adjacent transparentportions corresponding to the dense space patterns is deformed so as toreduce the quantity of the light in the opposite phase passing throughthe phase shifter. Thus, a photomask capable of good pattern formationcan be realized.

EMBODIMENT 3

A photomask according to Embodiment 3 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 17 is a plan view of the photomask of Embodiment 3. The photomaskof this embodiment is used for simultaneously forming a plurality offine contact patterns.

As shown in FIG. 17, on a transparent substrate 300, a semi-shieldingportion 301 is formed so as to cover a sufficiently large area. Also, inpositions in the semi-shielding portion 301 corresponding to desiredcontact patterns to be formed on a wafer through the exposure, atransparent portion 302, a pair of transparent portions 303 and 304 anda pair of transparent portions 305 and 306 are provided as openingpatterns. In this case, the transparent portion 302 is an openingpattern corresponding to an isolated contact pattern, and each of thetransparent portions 303 and 305 is an opening pattern corresponding toa contact pattern having another contact pattern closely disposed.Furthermore, around the transparent portion 302, auxiliary patternscorresponding to phase shifters 307 are provided with the semi-shieldingportion 301 sandwiched therebetween, for example, so as to be parallelto respective sides of the transparent portion 302 in the shape of asquare or a rectangle and to surround the transparent portion 302.Similarly, around each of the transparent portions 303 through 306,auxiliary patterns corresponding to phase shifters 308, 309, 310 or 311are provided with the semi-shielding portion 301 sandwichedtherebetween, for example, so as to be parallel to respective sides ofeach of the transparent portions 303 through 306 each in the shape of asquare or a rectangle and to surround the transparent portion 303, 304,305 or 306.

The phase shifters 307 provided around the transparent portion 302 aredisposed so as to attain a mask structure good for forming an isolatedcontact pattern. In this case, the phase shifter 307 has a width d0 andthe center line of the phase shifter 307 is away from the center of thetransparent portion 302 by a distance PW0.

Also, the transparent portion 303 is close to the different transparentportion 304 in one direction and is close to no transparent portion inthe other directions. In this case, one of the phase shifters 308provided around the transparent portion 303 in this one direction isdesignated as a phase shifter 308 a and the other phase shifters 308disposed in the other directions are designated as phase shifters 308 b.Furthermore, the transparent portion 305 is close to the differenttransparent portion 306 in one direction and is close to no transparentportion in the other directions. In this case, one of the phase shifters310 provided around the transparent portion 305 in this one direction isdesignated as a phase shifter 310 a and the other phase shifters 310disposed in the other directions are designated as phase shifters 310 b.

As a characteristic of this embodiment, assuming that a distance P1between the center of the transparent portion 303 and the center of thetransparent portion 304 is approximately 1.3×λ/NA, a distance PW1between the center of the phase shifter 308 a and the center of thetransparent portion 303 is set to satisfy PW1>PW0. In this case, adistance between the center of the phase shifter 308 b to the center ofthe transparent portion 303 is set to the distance PW0.

Furthermore, as another characteristic of this embodiment, assuming thata distance P2 between the center of the transparent portion 305 and thecenter of the transparent portion 306 is approximately 1.0×λ/NA, adistance PW2 between the center of the phase shifter 310 a and thecenter of the transparent portion 305 is set to satisfy PW2<PW0. In thiscase, a distance between the center of the phase shifter 310 b and thecenter of the transparent portion 305 is set to the distance PW0.

Specifically, in this embodiment, in the arrangement of phase shifters(auxiliary patterns) seen from the center of an opening pattern (atransparent portion), in the case where any different opening pattern isclose to this opening pattern, the position of a phase shifterpreferable for forming an isolated fine contact hole is changed inaccordance with the distance (close distance) between the close openingpatterns.

According to this embodiment, the contrast of the light intensitydistribution between the transparent portion and the auxiliary patterncan be emphasized by utilizing mutual interference between light passingthrough each transparent portion and light passing through the phaseshifters, namely, the auxiliary patterns, provided around thetransparent portion. Also, this effect to emphasize the contrast can beattained also in the case where a fine isolated space patterncorresponding to the transparent portion is formed by, for example, thepositive resist process using the oblique incident exposure.Accordingly, an isolated space pattern and an isolated line pattern ordense patterns can be simultaneously thinned by employing the obliqueincident exposure. Furthermore, even in the case where complicated andfine space patterns are close to each other, a pattern with a desireddimension can be satisfactorily formed.

Now, the photomask of this embodiment capable of satisfactorily formingan isolated contact hole and densely arranged contact holes will bedescribed in detail on the basis of results of simulation.

The plane structure of a photomask used in the simulation performed forconfirming the effect of this embodiment is the same as that (ofEmbodiment 2) shown in FIG. 10A. As shown in FIG. 10A, on a transparentsubstrate 250, a semi-shielding portion 251 is formed so as to cover asufficiently large area. Also, in positions in the semi-shieldingportion 251 corresponding to desired contact patterns to be formed on awafer through the exposure, a plurality of transparent portions 252 eachin the shape of a square with a side dimension W are provided to beadjacent to one another. Also, around each of the transparent portions252, phase shifters (auxiliary patterns) 253 are provided so as to havetheir center lines in positions away from the center of each transparentportion 252 by a distance PW0. In this case, each phase shifter 253 isin a rectangular shape with a width d and a length t. Furthermore, adistance between the center lines of the phase shifters 253 adjacent andclose to each other in an area between the adjacent transparent portions252 (hereinafter referred to as the adjacent shifter distance) isassumed to be a distance G.

FIG. 10B shows the profile of a light intensity distribution formedthrough the exposure using the photomask of FIG. 10A. In FIG. 10B, thelight intensity obtained at the center of the transparent portion 252 isexpressed as Ip, the light intensity obtained at the center between theadjacent transparent portions 252 is expressed as Is, and the lightintensity obtained in a position where the light intensity is minimum inthe periphery of the transparent portion 252 is expressed as Ib. In thiscase, the center between the adjacent transparent portions 252corresponds to the center between the adjacent phase shifters 253. Also,the light intensity simulation is performed under conditions of theexposure wavelength λ of 193 nm and the numerical aperture NA of 0.65.Furthermore, ⅔ annular illumination having the outer diameter with adegree of coherence of 0.8 and the inner diameter with a degree ofcoherence of 0.53 is assumed to be used. In addition, the transmittanceof the semi-shielding portion 201 is set to 6%.

Furthermore, in the photomask of FIG. 10A, in order that each contactpattern can be satisfactorily formed even in an isolated state, thewidth d of each phase shifter 253 is set to approximately 0.15×λ/NA(=approximately 44 nm) and the distance PW0 between the phase shifter253 and the transparent portion 252 is set to approximately 0.4×λ/NA(=approximately 120 nm). Moreover, in order to adjust the contact holesize to a desired size of 100 nm, the side dimension W of thetransparent portion 252 and the length t of the phase shifter 253 areset to 160 nm. The change, calculated through the simulation, of thelight intensity Ip (namely, the light intensity obtained at the centerof the transparent portion 252) of FIG. 10B in accordance with thechange of a distance P (=G+2×PW0) between the centers of the openingpatterns (transparent portions) 252 in the aforementioned mask structureis shown in a graph of FIG. 18A, wherein the value of the distance P isnormalized by λ/NA.

As shown in FIG. 18A, when the distance P between the centers of theopening patterns is 1.5×λ/NA or less, the light intensity Ip is abruptlylowered and becomes the minimum when the distance P is approximately1.3×λ/NA. Furthermore, when the distance P is 1.3×λ/NA or less, thelight intensity Ip starts to abruptly increase and becomes higher thanthat obtained when the transparent portion 252 is isolated (namely, whenthe distance P is infinite) when the distance P is approximately λ/NA.

As described also in Embodiment 2, when opening patterns (transparentportions) are close to each other, the width of the semi-shieldingportion sandwiched between adjacent phase shifters provided in an areabetween these opening patterns is so small that the quantity of light inthe positive phase passing through the photomask is reduced. Also, thelight intensity peak Ip obtained at the center of the opening pattern isformed by the light in the positive phase, and therefore, when thequantity of the light in the positive phase is reduced as describedabove, the light intensity Ip is lowered. Furthermore, since such aphenomenon is serious when the distance G between the adjacent phaseshifters is 0.5×λ/NA (see Embodiment 2), the phenomenon is serious whenthe distance P between the centers of opening patterns close to eachother (hereinafter referred to as close opening center distance) isG+2×PW0=0.5×λ/NA+2×0.4×λ/NA=1.3×λ/NA.

Furthermore, when one transparent portion is close to a differenttransparent portion, the quantity of the light in the positive phasepassing through the photomask is increased again owing to light in thepositive phase passing through the different transparent portion. Inthis case, the influence of the different transparent portion isremarkable when the distance P between the centers of these transparentportions (i.e., the close opening center distance) is λ/NA.

As described so far, when the close opening center distance P is in thevicinity of 1.3×λ/NA, the light intensity Ip obtained at the center ofthe transparent portion is lowered, but when the close opening centerdistance P is in the vicinity of λ/NA, the light intensity Ip obtainedat the center of the transparent portion is increased. It is noted thatwhen the light intensity Ip is lowered, the contrast is lowered,resulting in preventing good pattern formation. Furthermore, when thelight intensity Ip is increased, the size of a contact hole to be formedis increased, resulting in preventing fine pattern formation.

FIG. 18B shows the result of simulation similar to that performed forobtaining FIG. 10B, and specifically shows the light intensitydistribution formed in a position corresponding to line AB of thephotomask of FIG. 10A. FIG. 18B shows the results of the simulation forthe light intensity distribution profile obtained by respectivelysetting the close opening center distance P to 450 nm (=approximately1.5×λ/NA), 390 nm (=approximately 1.3×λ/NA) and 300 nm (=approximately1.0×λ/NA). As shown in FIG. 18B, when the close opening center distancesP are different, namely, when the closeness of adjacent opening patternsare different, the profiles of the light intensity distributionscorresponding to the centers of the respective opening patterns do notaccord with each other, and hence, fine contact patterns cannot beuniformly formed.

In contrast, the present inventor has found as a result of detailedsimulation that the light intensity profiles corresponding to thecenters of opening patterns can be made uniform regardless of the closeopening center distance P by changing the position of a phase shifterseen from the center of each opening pattern in accordance with theclose opening center distance P. Specifically, when the position of aphase shifter against the close opening center distance P for makinguniform the light intensity profiles corresponding to the centers of theopening patterns is expressed as PW(P), ΔPW(P) defined as(PW(P)−PW0)/PW0 (i.e., PW(P)=PW0+ΔPW(P)×PW0) is expressed as shown in agraph of FIG. 18C. Specifically, when the close opening center distanceP is in the vicinity of 1.3×λ/NA, the optimum position PW(P) of a phaseshifter against each close opening center distance P is preferably setto be larger by approximately 10% than a position PW0 of the phaseshifter for satisfactorily forming an isolated contact pattern. Also,when the close opening center distance P is in the vicinity of λ/NA, theposition PW(P) is preferably set to be smaller by approximately 10% thanthe position PW0.

Also, FIG. 18D shows the result of the simulation similar to thatperformed for obtaining FIG. 10B, and specifically shows the lightintensity distribution formed in the position corresponding to line ABin the photomask of FIG. 10A. FIG. 18D shows the results of thesimulation for the light intensity distribution profile obtained byusing the photomask in which a phase shifter is disposed in the positionshown in FIG. 18C respectively when the close opening center distance Pis 450 nm (=approximately 1.5×λ/NA), 390 nm (=approximately 1.3×λ/NA)and 300 nm (=approximately 1.0×λ/NA). As shown in FIG. 18D, when thephase shifter is disposed in the position shown in the graph of FIG.18C, the profiles of the light intensity distributions corresponding tothe centers of the opening patterns can be made to accord with eachother with respect to all the aforementioned values of the close centerline distance P.

On the basis of the results of these simulations, it can be understoodthat when there are a plurality of opening patterns (transparentportions) close to one another and each surrounded with phase shifters,the position PW seen from the center of the transparent portion of eachphase shifter is preferably set as follows in accordance with the closecenter line distance P:

First, when the close opening center distance P is in the vicinity of1.3×λ/NA, and more specifically, when 1.15×λ/NA<P<1.45×λ/NA, assumingthat a phase shifter provided on a side of an opening pattern close toanother opening pattern is disposed in a position PW1 seen from thecenter of the opening pattern and a phase shifter provided on anotherside of the opening pattern not close to another opening pattern isdisposed in a position PW0 seen from the center of the opening pattern,the position PW1 is preferably larger than the position PW0, and morepreferably, the position PW1 is larger than the position PW0 by 5% ormore.

Next, when the close opening center distance P is in the vicinity ofλ/NA, and more specifically, when 0.85×λ/NA<P<1.15×λ/NA, assuming that aphase shifter provided on a side of one opening pattern close to anotheropening pattern is disposed in a position PW2 seen from the center ofthe opening pattern and a phase shifter provided on another side of theopening pattern not close to another opening pattern is disposed in aposition PW0 seen from the center of the opening pattern, the positionPW2 is preferably smaller than the position PW0, and more preferably,the position PW2 is smaller than the position PW0 by 5% or more.

As described so far, according to this embodiment, in the case wheredense contact patterns are formed, the position of a phase shifterprovided in an area corresponding to the dense contact holes (namely,the distance of the phase shifter from the center of a transparentportion) is changed in accordance with the close distance of contactpatterns (namely, the close opening center distance P). As a result, aphotomask capable of forming a uniform light intensity distributionprofile in forming contact patterns with an arbitrary density can berealized. Accordingly, fine contact hole patterns arbitrarily arrangedcan be satisfactorily formed.

Also in this embodiment, the cross-sectional structure of the photomaskmay be, for example, any of the cross-sectional structures shown inFIGS. 6A through 6D described in Embodiment 1.

Modification of Embodiment 3

A photomask according to a modification of Embodiment 3 of the inventionwill now be described with reference to the accompanying drawings.

FIG. 19 is a plan view of the photomask of this modification. Thephotomask of this modification is used for simultaneously forming aplurality of fine line-shaped space patterns. Specifically, desiredpatterns to be formed in this modification are fine line-shaped spacepatterns differently from Embodiment 3 where the desired patterns arethe contact hole patterns.

As shown in FIG. 19, on a transparent substrate 350, a semi-shieldingportion 351 is formed so as to cover a sufficiently large area. Also, inthe semi-shielding portion 351, a transparent portion 352, a pair oftransparent portions 353 and 354 and a pair of transparent portions 355and 356 are provided in positions corresponding to the desired spacepatterns to be formed on a wafer through the exposure. In this case, thetransparent portion 352 is an opening pattern corresponding to anisolated space pattern, and each of the transparent portions 353 and 355is an opening pattern corresponding to a space pattern having anotherspace pattern closely disposed. Furthermore, auxiliary patternscorresponding to phase shifters 357 are provided around the transparentportion 352 with the semi-shielding portion 351 sandwiched therebetweenso as to be parallel to the respective long sides of the line-shapedtransparent portion 352. Similarly, auxiliary patterns corresponding tophase shifters 358 through 361 are provided respectively around thetransparent portions 353 through 356 with the semi-shielding portion 351sandwiched therebetween so as to be parallel to the respective longsides of the line-shaped transparent portions 353 through 356.

The phase shifters 357 provided around the transparent portion 352 arearranged so as to attain a mask structure good for forming an isolatedspace pattern, and each phase shifter 357 has a width d0 and a distancebetween the center line of the phase shifter 357 and the center of thetransparent portion 352 is a distance PG0.

The transparent portion 353 is close to the different transparentportion 354 in one direction and is not close to another transparentportion in the other directions. In this case, one of the phase shifters358 provided around the transparent portion 353 in this one direction isdesignated as a phase shifter 358 a and the other phase shifters 358provided around the transparent portion 353 in the other directions aredesignated as phase shifters 358 b. Furthermore, the transparent portion355 is close to the different transparent portion 356 in one directionand is not close to another transparent portion in the other directions.In this case, one of the phase shifters 360 provided around thetransparent portion 355 in this one direction is designated as a phaseshifter 360 a and the other phase shifters provided around thetransparent portion 355 in the other directions are designated as phaseshifters 360 b.

As a characteristic of this embodiment, when a distance P1 between thecenter of the transparent portion 353 and the center of the transparentportion 354 is approximately 1.15×λ/NA, a distance PG1 from the centerof the phase shifter 358 a to the center of the transparent portion 353is set to satisfy PG1>PG0. In this case, a distance from the center ofthe phase shifter 358 b to the center of the transparent portion 353 isset to the distance PG0.

Furthermore, as another characteristic of this embodiment, when adistance P2 between the center of the transparent portion 355 and thecenter of the transparent portion 356 is approximately 0.85×λ/NA, adistance PG2 from the center of the phase shifter 360 a to the center ofthe transparent portion 355 is set to satisfy PG2<PG0. In this case, adistance from the center of the phase shifter 360 b to the center of thetransparent portion 355 is set to the distance PG0.

Specifically, in this modification, with respect to the position of aphase shifter (auxiliary pattern) seen from the center of an openingpattern (transparent portion), when another opening pattern is close tothe opening pattern, the position of a phase shifter preferred forforming an isolated fine space pattern is changed in the same manner asin Embodiment 3 in accordance with the distance between these openingpatterns (the close opening center distance).

According to this modification, the contrast of the light intensitydistribution between the transparent portion and the auxiliary patterncan be emphasized by utilizing mutual interference between light passingthrough each transparent portion and light passing through the phaseshifters, namely, the auxiliary patterns, provided around thetransparent portion. Also, this effect to emphasize the contrast can beattained also in the case where a fine isolated space patterncorresponding to the transparent portion is formed by, for example, thepositive resist process using the oblique incident exposure.Accordingly, an isolated space pattern and an isolated line pattern ordense patterns can be simultaneously thinned by employing the obliqueincident exposure. Furthermore, even in the case where complicated andfine space patterns are close to each other, a pattern with a desireddimension can be satisfactorily formed.

Also in this modification, the profile of a light intensity distributioncorresponding to the center of an opening pattern (transparent portion)is changed in accordance with the close opening center distance due tothe influence of another opening pattern close to this opening patternas described in Embodiment 3. However, in this embodiment, since theopening pattern does not correspond to a contact pattern but correspondsto a line-shaped space pattern, the relationship between the closeopening center distance and the profile of the light intensitydistribution is different from that described in Embodiment 3.

FIG. 20A shows the dependency of the light intensity Ip obtained at thecenter of an opening pattern (a transparent portion) on the closeopening center distance P obtained through the same calculation carriedout for obtaining FIG. 18A of Embodiment 3. In FIG. 20A, the value ofthe close opening center distance P is normalized by λ/NA.

As shown in FIG. 20A, differently from Embodiment 3, the light intensityIp is the minimum when the close opening center distance P is in thevicinity of 1.15×λ/NA. Also, when the close opening center distance P isin the vicinity of 0.85×λ/NA, the light intensity Ip has a value largerthan that obtained when the transparent portion is isolated (i.e., whenthe close opening center distance P is infinite). In other words, whenthe close opening center distances P are different, namely, when thecloseness of adjacent opening patterns are different, the profiles ofthe light intensity distributions corresponding to the centers of therespective opening patterns do not accord with each other, and hence,fine contact patterns cannot be uniformly formed.

In contrast, the present inventor has found that the light intensityprofiles corresponding to the centers of opening patterns can be madeuniform regardless of the close opening center distance P by changingthe position of a phase shifter seen from the center of the openingpattern in accordance with the close opening center distance P.Specifically, when the position of a phase shifter against each closeopening center distance P for making uniform the light intensityprofiles corresponding to the centers of the opening patterns isexpressed as PW(P), ΔPW(P) defined as (PW(P)−PW0)/PW0 (i.e.,PW(P)=PW0+ΔPW(P)×PW0) is expressed as shown in a graph of FIG. 20B.Specifically, when the close opening center distance P is in thevicinity of 1.15×λ/NA, the optimum position PW(P) of a phase shifteragainst each close opening center distance P is preferably set to belarger by approximately 10% than a position PW0 of the phase shifter forsatisfactorily forming an isolated contact pattern. Also, when the closeopening center distance P is in the vicinity of 0.85×λ/NA, the positionPW(P) is preferably set to be smaller by approximately 10% than theposition PW0.

On the basis of the above description, it is found that when there are aplurality of line-shaped opening patterns close to one another, theposition PW of each phase shifter provided around the opening pattern(transparent portion) seen from the center of the transparent portion ispreferably set as follows in accordance with the close opening centerdistance P:

First, when the close opening center distance P is in the vicinity of1.15×λ/NA, and more specifically, when 1.0×λ/NA<P<1.3×λ/NA, assumingthat a phase shifter provided on a side of an opening pattern close toanother opening pattern is disposed in a position PG1 seen from thecenter of the opening pattern and that a phase shifter provided onanother side of the opening pattern not close to another opening patternis disposed in a position PG0 seen from the center of the openingpattern, the position PG1 is preferably larger than the position PG0,and more preferably, the position PG1 is larger than the position PG0 by5% or more.

Next, when the close opening center distance P is in the vicinity of0.85×λ/NA, and more specifically, when 0.7×λ/NA<P<1.0×λ/NA, assumingthat a phase shifter provided on one side of one opening pattern closeto another opening pattern is disposed in a position PG2 seen from thecenter of the opening pattern and that a phase shifter provided onanother side of the opening pattern not close to another opening patternis disposed in a position PG0 seen from the center of the openingpattern, the position PG2 is preferably smaller than the position PG0,and more preferably, the position PG2 is smaller than the position PG0by 5% or more.

As described so far, according to this modification, in the case wheredense space patterns are formed, the position of a phase shifterprovided in an area corresponding to the dense space patterns (namely,the distance of the phase shifter from the center of a transparentportion) is changed in accordance with the close distance of contactpatterns (namely, the close opening center distance P). As a result, aphotomask capable of forming a uniform light intensity distributionprofile in forming space patterns with an arbitrary density can berealized. Accordingly, fine space patterns arbitrarily arranged can besatisfactorily formed.

EMBODIMENT 4

A photomask according to Embodiment 4 of the invention will now bedescribed with reference to the accompanying drawings.

FIG. 21A is a plan view of the photomask of Embodiment 4. The photomaskof this embodiment is used for forming a fine line-shaped space pattern.

As shown in FIG. 21A, on a transparent substrate 400, a semi-shieldingportion 401 is formed so as to cover a sufficiently large area. Also, inthe semi-shielding portion 401, in a position corresponding to a desiredspace pattern to be formed on a wafer through the exposure, aline-shaped opening pattern is formed as a transparent portion 402.Furthermore, around the transparent portion 402, auxiliary patternscorresponding to phase shifters 403 and 404 are provided so as tosurround the transparent portion 402 with the semi-shielding portion 401sandwiched therebetween. Specifically, one pair of phase shifters 403are provided so as to sandwich the transparent portion 402 and to beparallel to the transparent portion 402 along the lengthwise direction(line direction) of the transparent portion 402, and another pair ofphase shifters 404 are provided so as to sandwich the transparentportion 402 and to be parallel to the transparent portion 402 along thewidth direction of the transparent portion 402.

In this case, the pair of phase shifters 403 are arranged, for obtaininga mask structure good for forming an isolated space pattern, in such amanner that a distance between the phase shifters 403 with thetransparent portion 402 sandwiched therebetween (more precisely, adistance between the center lines of the phase shifters 403) is adistance PW0×2.

As a characteristic of this embodiment, the phase shifters 403 areshorter than the transparent portion 402 along the line direction of thetransparent portion 402, namely, the ends (line ends) along thelongitudinal direction of the transparent portion 402 are protrudedbeyond the line ends of the phase shifters 403. The phase shifters 404opposing the line ends of the transparent portion 402 may be longer orshorter than the width (line width) of the transparent portion 402.

According to Embodiment 4, the following effect can be attained inaddition to the effects of Embodiments 1 through 3 above: In general, informing a line-shaped pattern by using an opening pattern (transparentportion), the quantity of light passing through a line end of thepattern is reduced, and hence, the line end of the pattern formed afterthe exposure is receded, resulting in reducing the length of the line.In contrast, in this embodiment, parts of the phase shifters surroundingthe line ends of the opening pattern are removed, so as to increase thequantity of light passing through the opening pattern. As a result, theline end of a pattern formed after the exposure (hereinafter referred toas a transferred pattern) can be prevented from receding.

FIG. 21B shows results of pattern formation simulation performed byusing the photomask of FIG. 21A in which the line ends of thetransparent portion 402 are protruded beyond the line ends of the phaseshifters 403 by a dimension Z set to 0 nm and 100 nm. On the abscissa ofFIG. 21B, a position with the scale of 0 (zero) corresponds to the endof the transparent portion (opening pattern) 402. Also, in FIG. 21B, apattern shape obtained when the dimension Z is 100 nm is shown with asolid line and a pattern shape obtained when the dimension Z is 0 nm isshown with a broken line. As shown in FIG. 21B, in the phase shiftersprovided in parallel to the opening pattern, when the parts thereofdisposed in the vicinity of the line ends of the opening pattern areremoved, the line ends of the transferred pattern (resist pattern) canbe prevented from receding.

Now, a result of simulation performed for quantifying the part of thephase shifter to be removed in the vicinity of the line end of theopening pattern for preventing the line end of the transferred patternfrom receding will be described.

FIG. 22A is a plan view of a photomask used in the simulation. In FIG.22A, like reference numerals are used to refer to like elements shown inFIG. 21A so as to omit the description.

As shown in FIG. 22A, with respect to each of a pair of line-shapedtransparent portions (opening patterns) 402 having a width L andopposing each other at their line ends, a pair of phase shifters 403with a width d are provided along the line direction of the transparentportion 402 so as to sandwich each transparent portion 402 therebetween.In this case, it is assumed that a distance between the center lines ofthe phase shifters 403 sandwiching the transparent portion 402 is adistance 2×PW. Also, it is assumed that a part of the phase shifter 403removed in the vicinity of the line end of the transparent portion 402has a dimension Z.

FIG. 22B shows a pattern shape resulting from the exposure using thephotomask of FIG. 22A. In FIG. 22B, it is assumed that a distancebetween line ends of a pair of transferred patterns (resist patterns)corresponding the pair of transparent portions 402 is a distance V.

FIG. 22C shows a result of light intensity simulation carried out forcalculating the distance V between the line ends of the transferredpatterns (hereinafter referred to as a pattern distance) with thedimension Z (hereinafter referred to as the shifter removal dimension)variously set in the photomask of FIG. 22A with the width L set to 110nm, the distance 2×PW set to 180 nm and the width d set to 30 nm. Inthis light intensity simulation, the exposure is performed with theexposure wavelength λ of 193 nm and the numerical aperture NA of 0.7.Also, as the illumination, ⅔ annular illumination having the outerdiameter with a degree of coherence of 0.8 and the inner diameter with adegree of coherence of 0.53 is assumed to be used. Furthermore, thetransmittance of the semi-shielding portion 401 is 6%. In FIG. 22C, theabscissa indicates the shifter removal dimension Z and the value of theshifter removal dimension Z is normalized by λ/NA. Also, in FIG. 22C,the ordinate indicates the pattern distance V.

As shown in FIG. 22C, when the shifter removal dimension Z is 0 (zero),the pattern distance V is approximately 160 nm, and as the shifterremoval dimension Z is increased, the pattern distance V is reduced,namely, the recession of the line end of the transferred pattern isreduced. In this case, when the shifter removal dimension Z exceeds0.1×λ/NA, the pattern distance V is approximately 120 nm and is notfurther reduced. Furthermore, when the shifter removal dimension Z is0.03×λ/NA, the pattern distance V is reduced to approximately 140 nm.This reveals that the effect of this embodiment can be attained alsowhen the shifter removal dimension Z is approximately 0.03×λ/NA.

Accordingly, in this embodiment, in order to prevent the line end of thetransferred pattern from receding, a mask structure in which the lineend of the line-shaped opening pattern is protruded beyond the phaseshifter provided in parallel to the opening pattern by a given or largerdimension is preferably used. Specifically, the given dimension ispreferably approximately 0.1×λ/NA but this effect can be attained evenwhen the given dimension is approximately 0.03×λ/NA.

In other words, the line end of the line-shaped opening pattern ispreferably protruded beyond the phase shifter by a dimension ofapproximately 0.03×λ/NA or more. However, in order to effectivelyutilize the principle of the outline enhancement method, the dimension Zof the protruded part of the opening pattern is preferably approximately0.5×λ/NA or less. This is for the following reason: Since a phaseshifter is preferably provided in a position away from an openingpattern by a distance of approximately 0.5×λ/NA or less, whichcorresponds to light interference distance, the dimension of theprotruded part of the line end of the opening pattern, namely, thelength of the part where the phase shifter is not provided in parallelto the opening pattern, is preferably 0.5×λ/NA or less.

As described so far, according to this embodiment, in the case where aline-shaped space pattern is formed, in the relationship between aline-shaped opening pattern and phase shifters provided around theopening pattern, the line end of the opening pattern is protruded beyondthe line end of a phase shifter disposed in parallel to the openingpattern along the line direction, so that the line end of theline-shaped space pattern can be prevented from receding.

Also in this embodiment, the photomask may have, for example, any of thecross-sectional structures shown in FIGS. 6A through 6D described inEmbodiment 1.

Modification of Embodiment 4

A photomask according to a modification of Embodiment 4 of the inventionwill now be described with reference to the accompanying drawings.

FIG. 23A is a plan view of the photomask of the modification ofEmbodiment 4. The photomask of this modification is used for forming afine line-shaped space pattern.

As shown in FIG. 23A, on a transparent substrate 400, a semi-shieldingportion 401 is formed so as to cover a sufficiently large area. Also, inthe semi-shielding portion 401, in a position corresponding to a desiredspace pattern to be formed on a wafer through the exposure, aline-shaped opening pattern is formed as a transparent portion 402.Furthermore, around the transparent portion 402, auxiliary patternscorresponding to phase shifters 403 and 404 are provided so as tosurround the transparent portion 402 with the semi-shielding portion 401sandwiched therebetween. Specifically, one pair of phase shifters 403are provided so as to sandwich the transparent portion 402 and to beparallel to the transparent portion 402 along the lengthwise direction(line direction) of the transparent portion 402, and another pair ofphase shifters 404 are provided so as to sandwich the transparentportion 402 and to be parallel to the transparent portion 402 along thewidth direction of the transparent portion 402.

As a characteristic of this modification, each phase shifter 403extending along the line direction is composed of a phase shifter 403 aprovided in parallel to a line center part (more precisely, a part otherthan a line end part described below) of the transparent portion 402 anda phase shifter 403 b provided in parallel to the line end part (moreprecisely, a part with a dimension Z of 0.1×λ/NA from the line end) ofthe transparent portion 402. In this case, a pair of phase shifters 403a sandwiching the line center part of the transparent portion 402 arearranged, for obtaining a mask structure good for forming an isolatedspace pattern, in such a manner that a distance between the phaseshifters 403 a with the transparent portion 402 sandwiched therebetween(more precisely, a distance between the center lines of the phaseshifters 403 a) is a distance PW0×2. On the other hand, a pair of phaseshifters 403 b sandwiching the line end part of the transparent portion402 are arranged in such a manner that a distance between the phaseshifters 403 b with the transparent portion 402 sandwiched therebetween(more precisely, a distance between the center lines of the phaseshifters 403 b) is a distance PWZ×2, whereas PWZ×2>PW0×2. Also, eachphase shifter 404 opposing the line end of the transparent portion 402may be longer or shorter than the width (line width) of the transparentportion 402.

In Embodiment 4, the parts of the phase shifters 403 surrounding theline ends of the transparent portion 402 are removed, so as to increasethe quantity of light passing through the transparent portion 402 (seeFIG. 21A). In contrast, in this modification, parts of the phaseshifters 403 surrounding the line ends of the transparent portion 402,namely, the phase shifters 403 b, are disposed in positions farther fromthe transparent portion 402 (opening pattern), so as to increase thequantity of light passing through the opening pattern, therebypreventing the line ends of a transferred pattern from receding.

Thus, this modification can attain the same effect as that of Embodiment4.

FIG. 23B shows a shape of a resist pattern formed through the exposureusing the photomask of FIG. 23A obtained through simulation. On theabscissa of FIG. 23B, a position with the scale of 0 (zero) correspondsto the end of the transparent portion (open pattern) 402. Also, in FIG.23B, a pattern shape obtained when the distance PWZ is equal to thedistance PW0 (namely, when the phase shifter 403 b is not farther fromthe transparent portion 402) is shown with a broken line and a patternshape obtained when the distance PWZ is set to 1.2×PW0 (namely, when thephase shifter 403 b is farther from the transparent portion 402) isshown with a solid line. The dimension Z of the phase shifter 403 b isset to 0.1×λ/NA (=approximately 270 nm). As shown in FIG. 23B, in thephase shifters provided in parallel to the opening pattern, when theparts disposed in the vicinity of the line ends of the opening patternare disposed to be farther from the opening pattern, the line ends ofthe transferred pattern (resist pattern) can be prevented from receding.

Now, a result of simulation performed for quantifying the part, in thevicinity of the line end of the opening pattern, of the phase shifter tobe disposed farther from the opening pattern for preventing the line endof the transferred pattern from receding will be described.

FIG. 24A is a plan view of a photomask used in the simulation. In FIG.24A, like reference numerals are used to refer to like elements shown inFIG. 23A so as to omit the description. The photomask of FIG. 24A has asimilar structure to the photomask of Embodiment 4 shown in FIG. 22Aexcept that each phase shifter 403 b is provided in parallel to a partwith the dimension Z from the line end of the opening pattern(transparent portion) 402.

In this case, a distance between the center lines of the pair of phaseshifters 403 b sandwiching the line end part of the transparent portion402 is a distance 2×PWZ. Also, a distance between the center lines ofthe pair of phase shifters 403 a sandwiching the line center part of thetransparent portion 402 is a distance 2×PW.

FIG. 24B shows a pattern shape resulting from the exposure using thephotomask of FIG. 24A. In FIG. 24B, it is assumed that a distancebetween line ends of a pair of transferred patterns (resist patterns)corresponding to the pair of transparent portions 402 is a distance V.

FIG. 24C shows a result of light intensity simulation carried out forcalculating the distance (pattern distance) V between the line ends ofthe transferred patterns with the distance 2×PWZ (hereinafter referredto as the shifter distance) variously set in the photomask of FIG. 24Awith the width L set to 110 nm, the distance 2×PW set to 180 nm, thewidth d set to 30 nm and the dimension Z set to 270 nm. In this lightintensity simulation, the exposure is performed with the exposurewavelength λ of 193 nm and the numerical aperture NA of 0.7. Also, asthe illumination, ⅔ annular illumination having the outer diameter witha degree of coherence of 0.8 and the inner diameter with a degree ofcoherence of 0.53 is assumed to be used. Furthermore, the transmittanceof the semi-shielding portion 401 is 6%. In FIG. 24C, the abscissaindicates 2×(PWZ−PW), that is, increment of the shifter distance 2×PWZ,normalized by λ/NA, and the ordinate indicates the pattern distance V.

As shown in FIG. 24C, when 2×(PWZ−PW) is 0 (zero), the pattern distanceV is approximately 160 nm, and as 2×(PWZ−PW) is increased, the patterndistance V is reduced, namely, the recession of the line end of thetransferred pattern is reduced. In this case, when the value of2×(PWZ−PW) exceeds 0.1×λ/NA, the pattern distance V is approximately 120nm and is not further reduced. Furthermore, when the value of 2×(PWZ−PW)is 0.03×λ/NA, the pattern distance V is reduced to approximately 140 nm.This reveals that the effect of this modification can be attained alsowhen 2×(PWZ−PW) is approximately 0.03×λ/NA.

Accordingly, in this modification, in order to prevent the line end of atransferred pattern from receding, a mask structure in which a distance2×PWZ between a pair of phase shifters provided in parallel to the lineend part of a line-shaped opening pattern is larger than a distance 2×PWbetween a pair of phase shifters provided in parallel to the line centerpart of the opening pattern by a given or larger dimension is preferablyused. Specifically, the given dimension is preferably approximately0.1×λ/NA but this effect can be attained even when the given dimensionis approximately 0.03×λ/NA.

In other words, 2×(PWZ−PW) is preferably approximately 0.03×λ/NA ormore. However, in order to effectively utilize the principle of theoutline enhancement method, PWZ−L/2 is preferably approximately 0.5×λ/NAor less. This is for the following reason: Since a phase shifter ispreferably provided in a position away from an opening pattern by adistance of approximately 0.5×λ/NA or less, which corresponds to lightinterference distance, PWZ−L/2, namely, the distance of the phaseshifter from the opening pattern, is preferably 0.5×λ/NA or less.

In this modification, similarly to Embodiment 4, the dimension Z(namely, the length of the phase shifter 403 b) is preferably not lessthan approximately 0.03×λ/NA and not more than approximately 0.5×λ/NA.

EMBODIMENT 5

A pattern formation method according to Embodiment 5 of the invention,and more specifically, a pattern formation method using a photomaskaccording to any of Embodiments 1 through 4 (and modifications of theseembodiments) (hereinafter referred to as the present photomask), will bedescribed with reference to the accompanying drawings.

FIGS. 25A through 25D are cross-sectional views for showing proceduresin the pattern formation method of this embodiment.

First, as shown in FIG. 25A, a target film 501 of, for example, a metalfilm or an insulating film is formed on a substrate 500. Thereafter, asshown in FIG. 25B, for example, a positive resist film 502 is formed onthe target film 501.

Next, as shown in FIG. 25C, the resist film 502 is irradiated withexposing light 503 through the present photomask, such as the photomaskaccording to Embodiment 1 shown in FIG. 2A (more specifically, thephotomask having the cross-sectional structure of FIG. 6C). Thus, theresist film 502 is exposed to the exposing light 503 having passedthrough the photomask.

On the transparent substrate 100 of the photomask used in the procedureshown in FIG. 25C, the semi-shielding film (thin film) 107 correspondingto the semi-shielding portion is formed, and in the semi-shielding film107, the opening corresponding to a contact pattern to be transferredthrough the exposure is formed. Furthermore, in the semi-shielding film107 around the opening, other openings corresponding to phase shifterforming regions are provided, and the transparent substrate 100 below(above in the drawings) each of these other openings is trenched, so asto form the phase shifters corresponding to auxiliary patterns.

In this embodiment, in the exposure performed in FIG. 25C, the resistfilm 502 is subjected to the exposure by using an oblique incidentexposure light source. In this case, since the semi-shielding portionhaving low transmittance is used as the shielding pattern, the entireresist film 502 is exposed at weak energy. However, as shown in FIG.25C, it is only a latent image portion 502 a of the resist film 502corresponding to the contact pattern, namely, the opening (transparentportion) of the photomask, that is irradiated at exposure energysufficiently high for allowing the resist to dissolve in subsequentdevelopment.

Next, as shown in FIG. 25D, the resist film 502 is developed so as toremove the latent image portion 502 a. Thus, a resist pattern 504 havinga fine contact pattern is formed.

According to Embodiment 5, since the pattern formation method is carriedout by using the present photomask (specifically, the photomaskaccording to Embodiment 1), the same effects as those described inEmbodiment 1 can be attained. Specifically, the substrate (wafer) onwhich the resist is applied is subjected to the oblique incidentexposure through the present photomask. At this point, since the phaseshifters are arranged on the photomask so as to maximize the depth offocus and the exposure margin, a fine contact pattern with a large depthof focus and a large exposure margin can be formed.

Although the photomask according to Embodiment 1 is used in Embodiment5, in the case where a photomask according to any of Embodiments 2through 4 is used instead, the same effects as those described in thecorresponding embodiment can be attained.

Although the positive resist process is employed in Embodiment 5, thesame effects can be attained by employing the negative resist processinstead.

In Embodiment 5, oblique incident illumination (off-axis illumination)is preferably used in the procedure shown in FIG. 25C for irradiatingthe resist film. Thus, the exposure margin and the focus margin in thepattern formation can be improved. In other words, a fine pattern can beformed with a good defocus characteristic.

Furthermore, herein, the oblique incident light source means a lightsource as shown in any of FIGS. 26B through 26D obtained by removing avertical incident component from a general exposure light source of FIG.26A. Typical examples of the oblique incident light source are anannular exposure light source of FIG. 26B and a quadrupole exposurelight source of FIG. 26C. In the case where a contact pattern is formed,the annular exposure light source is preferably used. Alternatively, inthe case where a line-shaped space pattern is formed, the quadrupoleexposure light source is preferably used. Furthermore, in the case wherea contact pattern and a line-shaped space pattern are both formed, anannular/quadrupole exposure light source of FIG. 26D is preferably used.As a characteristic of this annular/quadrupole exposure light source,assuming the XY coordinate system with the center of the light source(the center of a general exposure light source) corresponding to theorigin, the annular/quadrupole exposure light source has acharacteristic of the quadrupole exposure light source when portions atthe center and on the X and Y axes of the light source are removed, andhas a characteristic of the annular exposure light source when theoutline of the light source is in a circular shape.

In the case where the annular exposure light source, namely, annularillumination, is employed, the light source preferably has an outerdiameter of 0.7 or more. Herein, the illumination radius of a reductionprojection aligner is indicated by using a unit normalized by thenumerical aperture NA. This is a value corresponding to interference inthe general illumination (the general exposure light source). Now, thereason why the light source with the outer diameter of 0.7 or more ispreferably used will be described in detail.

FIGS. 27A through 27E are diagrams for explaining the dependency,obtained through simulation, of an exposure characteristic of thepresent photomask on the diameter of the annular illumination.

FIG. 27A is a plan view of a photomask used in the simulation. As shownin FIG. 27A, a semi-shielding portion 511 is formed on a transparentsubstrate 510 so as to cover a sufficiently large area. In thesemi-shielding portion 511, an opening pattern corresponding to atransparent portion 512 is formed in a position corresponding to adesired contact pattern to be formed on a wafer through the exposure.Also, auxiliary patterns corresponding to phase shifters 513 areprovided around the transparent portion 512, for example, so as to beparallel to respective sides of the transparent portion 512 in a squareshape or a rectangular shape.

It is assumed that the transparent portion 512 has a side dimension W of130 nm, that each phase shifter 513 has a width d of 40 nm and that adistance PG between a pair of phase shifters 513 sandwiching thetransparent portion 512 is 220 nm. Also, the exposure is performed inthe simulation under conditions of the exposure wavelength λ of 193 nmand the numerical aperture NA of 0.7. In other words, various values areset in the simulation so as to obtain an optimum photomask for theillumination system.

FIG. 27B shows the annular illumination (annular exposure light source)used in the exposure using the photomask of FIG. 27A. As shown in FIG.27B, the inner diameter of the annular illumination is indicated by S1and the outer diameter thereof is indicated by S2, whereas the diametersS1 and S2 are expressed by using values normalized by the numericalaperture NA.

FIG. 27C shows a light intensity distribution formed on a wafer (in aposition corresponding to line AA′ of FIG. 27A) through the exposureusing the photomask of FIG. 27A performed by using the annularillumination of FIG. 27B. As shown in FIG. 27C, a peak value of thelight intensity obtained in a position corresponding to the opening(transparent portion 512) of the photomask of FIG. 27A is indicated byIo. As the peak intensity Io is higher, an optical image with highercontrast can be formed.

FIG. 27D is a graph obtained by plotting the values of the peakintensity Io obtained through simulation in which a value S2−S1 is fixedto 0.01 and a value (S1+S2)/2 is changed from 0.4 to 0.95 in the annularillumination of FIG. 27B. As shown in FIG. 27D, in the presentphotomask, as an illumination region (light source region) of theannular illumination is distributed in an area farther from the centerof the illumination system (light source), the contrast is higher.

FIG. 27E is a graph obtained by plotting the values of the depth offocus (DOF) obtained through simulation in which a contact hole patternwith a dimension of 100 nm is formed by using the photomask of FIG. 27Awith the value (S2−S1) fixed to 0.01 and the value (S1+S2)/2 changedfrom 0.4 to 0.95 in the annular illumination of FIG. 27B. As shown inFIG. 27E, in the present photomask, when the illumination region of theannular illumination is distributed in an area away from the center ofthe illumination system by 0.7 or more, the depth of focus is themaximum.

Specifically, it is understood from the results shown in the graphs ofFIGS. 27D and 27E that the illumination region of the annularillumination preferably includes a region away from the center of theillumination system by 0.7 or more in order to simultaneously attainhigh contrast and a large depth of focus.

EMBODIMENT 6

A mask data creation method according to Embodiment 6 of the inventionwill now be described with reference to the accompanying drawings. Inthis embodiment, mask data for a photomask according to any ofEmbodiments 1 through 4 (hereinafter referred to as the presentphotomask) is created.

Before describing a specific flow of the mask data creation method,conditions for realizing highly accurate pattern dimension control byusing the present photomask will be described.

In the present photomask, a dimension of a pattern to be formed afterexposure, namely, a CD (critical dimension), depends upon both a phaseshifter (auxiliary pattern) and a transparent portion. However, wheneither of the transparent portion and the phase shifter is fixed, apossible pattern dimension is determined.

The following description is given by exemplifying a photomask shown inFIG. 28. As shown in FIG. 28, a semi-shielding portion 601 is formed ona transparent substrate 600 so as to cover a sufficiently large area. Anopening pattern corresponding to a transparent portion 602 is providedin a position in the semi-shielding portion 601 corresponding to adesired contact pattern to be formed on a wafer through the exposure.Also, auxiliary patterns corresponding to phase shifters 603 areprovided around the transparent portion 602 with the semi-shieldingportion 601 sandwiched therebetween, for example, so as to be parallelto respective sides of the transparent portion 602 in a square shape ora rectangular shape. It is assumed that the transparent portion 602 hasa width W. Also, in this embodiment, among the phase shifters 603surrounding the transparent portion 602, phase shifters 603 paring witheach other with the transparent portion 603 sandwiched therebetween aredesignated as outline shifters, and a distance (between the inner sides)of the outline shifters is designated as an internal distance PG of theoutline shifters.

In such a photomask, when the internal distance PG is fixed to a valuePGC, the maximum CD realizable by this photomask is determined. In thisphotomask, the CD is changed in proportion to the width W, and the widthW never exceeds the value PGC. Accordingly, a CD attained when the widthW is the value PGC is the possible maximum CD. Herein, the maximum CDdetermined when the internal distance PG of the outline shifters isdetermined is designated as the allowable maximum CD.

On the contrary, when the width W is fixed to a value WC in thephotomask, the minimum CD realizable by the photomask is determined. Inthis photomask, the CD is changed in proportion to the internal distancePG, and the internal distance PG never becomes smaller than the valueWC. Accordingly, a CD attained when the internal distance PG is thevalue WC is the possible minimum CD. Herein, the minimum CD determinedwhen the width W is determined is designated as the allowable minimumCD.

Accordingly, in this embodiment, the internal distance PG is determinedat the first stage so that the maximum allowable CD obtained based on adesired CD can be larger than the desired CD, and thereafter, the widthW for realizing the desired CD is highly accurately calculated inconsideration of an accurate close relationship between patterns. Inthis manner, it is possible to realize a mask data creation method inwhich a pattern dimension can be highly accurately controlled.

Now, the flow of the mask data creation method of this embodiment willbe described in detail.

FIG. 29 is a basic flowchart for the mask data creation method of thisembodiment. Also, FIGS. 30A through 30C, 31A and 31B are diagrams ofexemplified mask patterns formed in respective procedures of the maskdata creation method of this embodiment.

FIG. 30A shows a desired pattern to be formed by the present photomask,and more specifically, shows an example of a design patterncorresponding to transparent portions (openings) of the presentphotomask. Specifically, patterns 701 through 703 shown in FIG. 30A arepatterns corresponding to regions of a resist to be sensitized throughthe exposure using the present photomask.

It is noted that the positive resist process is assumed to be employedin the pattern formation of this embodiment unless otherwise mentioned.In other words, the description is given on the assumption that anexposed region of a resist is removed through development and anunexposed region of the resist remains as a resist pattern. Accordingly,when the negative resist process is employed instead of the positiveresist process, the description can be similarly applied by assumingthat an exposed region of a resist remains as a resist pattern and anunexposed region is removed.

First, in step S1, the desired patterns 701 through 703 of FIG. 30A areinput to a computer used for the mask data creation. At this point, thetransmittances of a phase shifter and a semi-shielding portion used inthe mask pattern are respectively set.

Next, in step S2, the internal distance of outline shifters necessaryfor each of the desired patterns 701 through 703 is estimated on thebasis of exposure conditions and mask parameters such as thetransmittances of the phase shifter and the semi-shielding portion. Atthis point, the internal distance of each pair of outline shifters ispreferably set with respect to each pattern (i.e., each desired exposedregion in the resist) in consideration of the close relationship betweenthe respective patterns (hereinafter referred to as the pattern closerelationship). However, the necessary condition is that the allowablemaximum CD determined correspondingly to the internal distance of theoutline shifters is larger than the desired CD and therefore, theinternal distance of the outline shifters can be set, for example, byuniformly increasing the desired CD, whereas the desired CD should beincreased by a value exceeding the CD that changes depending upon thepattern close relationship.

Next, in step S3, the outline shifters are created. At this point, theinternal distance PG of the outline shifters is one determined in stepS2. Also, at this point, the width of each outline shifter is preferablychanged in accordance with the pattern close relationship, but the widthmay be uniformly set if the margin of a pattern formation characteristicfalls within an allowable range. However, in the case where a distancebetween outline shifters (i.e., phase shifters) respectivelycorresponding to adjacent patterns is as small as an allowable value orless of a mask processing characteristic, these outline shifters may becombined to create one phase shifter. Specifically, as shown in, forexample, FIG. 30B, outline shifters 711 through 714 are createdcorrespondingly to the desired patterns 701 through 703. In this case,the outline shifters 711 through 713 are outline shifters respectivelypeculiar to and corresponding to the desired patterns 701 through 703.Also, the outline shifter 714 is created by combining outline shiftersrespectively corresponding to the desired patterns 702 and 703. In otherwords, the outline shifter 714 is an outline shifter shared between thedesired patterns 702 and 703.

Next, in step S4, preparation is made for processing for adjusting thedimension of the mask pattern so that a pattern with a desired dimensioncan be formed correspondingly to the opening pattern (the transparentportion) of the photomask through the exposure using the presentphotomask (namely, OPC processing). In this embodiment, since the phaseshifters (outline shifters) have been determined in step S3, thedimensions of the transparent portions alone are adjusted in the OPCprocessing, thereby creating photomask data for realizing the desiredCD. Therefore, for example, as shown in FIG. 30C, opening patterns 721through 723 corresponding to the transparent portions are set on theinsides of the outline shifters 711 through 714 created in step S3, andthe opening patterns 721 through 723 are set as CD adjustment patterns.At this point, the desired patterns 701 through 703 are set as targetpatterns to be formed. Also, the outline shifters 711 through 714 arenot deformed for the CD adjustment but are set as patterns present onthe mask and as reference patterns to be referred to in CD prediction.

Next, in step S5, as shown in FIG. 31A, a semi-shielding portion 750 forpartially transmitting exposing light in the identical phase withrespect to the opening patterns 721 through 723 is set as the backgroundof the photomask, namely, on the outsides of the opening patterns 721through 723 and the outline shifters 711 through 714. It is noted thatthe outline shifters 711 through 714 are set as phase shifters fortransmitting the exposing light in the opposite phase with respect tothe opening patterns 721 through 723.

Subsequently, in steps S6, S7 and S8, the OPC processing (such as modelbase OPC processing) is carried out. Specifically, in step S6, adimension of a resist pattern (more strictly, a dimension of an exposedregion of the resist) formed by using the present photomask is predictedthrough simulation performed in consideration of the optical principle,a resist development characteristic, and an etching characteristic orthe like if necessary. Subsequently, in step S7, it is determinedwhether or not the predicted dimension of the pattern accords with thedimension of the desired target pattern. When the predicted dimensiondoes not accord with the desired dimension, the CD adjustment pattern isdeformed in step S8 on the basis of a difference between the predicteddimension and the desired dimension, so as to deform the mask pattern.

As a characteristic of this embodiment, the outline shifters forrealizing the desired CD are previously determined in step S3, and theCD adjustment patterns set in step S4 alone are deformed in steps S6through S8, so as to obtain the mask pattern for forming the patternwith the desired dimension. Specifically, the procedures in steps S6through S8 are repeated until the predicted dimension of the patternaccords with the desired dimension, so that the mask pattern for formingthe pattern with the desired dimension can be ultimately output in stepS9. FIG. 31B shows an example of the mask pattern output in step S9.

When the present photomask having the mask pattern created by the maskdata creation method of Embodiment 6 is used in the exposure of a waferon which a resist has been applied, contrast of light passing throughthe opening patterns is emphasized by the outline shifters providedaround the opening patterns. Therefore, fine space patterns can beformed in regions of the resist corresponding to the opening patterns.

Furthermore, since an outline enhancement mask that can definitelyrealize a desired CD can be created in Embodiment 6, a fine spacepattern can be accurately formed in a desired dimension.

In step S2 of this embodiment, the internal distance of the outlineshifters is set by uniformly increasing the desired CD. However, asdescribed in Embodiment 3, in order to attain a good pattern formationcharacteristic, a distance from the center of an opening pattern to aphase shifter is preferably changed in accordance with the pattern closerelationship. Specifically, in Embodiment 3, the preferable position ofa phase shifter is defined by using a distance from the center of theopening pattern to the center line of the phase shifter. Accordingly, inthis embodiment, when the internal distance of the outline shifters iscalculated on the basis of this distance, mask pattern data of aphotomask exhibiting a better fine pattern formation characteristic canbe created.

Furthermore, in step S3 of this embodiment, the widths of the outlineshifters provided around the respective desired patterns are uniformlyset. However, as described in Embodiment 2, the widths of the outlineshifters are more preferably changed in accordance with the patternclose relationship. Specifically, also in this embodiment, when thewidth of each outline shifter, namely, each phase shifter, is changed inaccordance with the distance to an adjacent outline shifter as describedin Embodiment 2, mask pattern data of a photomask exhibiting a betterfine pattern formation characteristic can be created.

Although the width of the phase shifter is determined after determiningthe internal distance of the outline shifters in Embodiment 6, theinternal distance of the outline shifters may be determined afterdetermining the width of the phase shifter instead.

Moreover, in Embodiment 6, the description is given with respect to atransmission photomask, which does not limit the invention. The presentinvention is applicable to a reflection mask by replacing thetransmission phenomenon of exposing light with the reflection phenomenonby, for example, replacing the transmittance with reflectance.

1-42. (canceled)
 43. A pattern formation method using a photomask,comprising the steps of: (a) forming a resist film on a substrate; (b)irradiating said resist film with the exposing light through saidphotomask, and (c) forming a resist pattern by developing said resistfilm after irradiation with the exposing light, wherein said photomaskcomprises, on a transparent substrate: a semi-shielding portion having atransmitting property against exposing light; a transparent portionsurrounded with said semi-shielding portion and having a transmittingproperty against the exposing light; and an auxiliary pattern surroundedwith said semi-shielding portion and provided around said transparentportion, wherein part of said semi-shielding portion is interposedbetween said transparent portion and said auxiliary pattern, saidtransparent portion is smaller than a rectangle with a side of(0.8×λ×M)/NA, said auxiliary pattern is a rectangular pattern and has acenter line thereof in a position away from the center of saidtransparent portion by a distance not less than (0.3×λ×M)/NA and notmore than (0.5×λ×M)/NA, said semi-shielding portion and said transparentportion transmit the exposing light in an identical phase with respectto each other, said auxiliary pattern transmits the exposing light in anopposite phase with respect to said semi-shielding portion and saidtransparent portion and is not transferred through exposure, and λindicates a wavelength of the exposing light, and M and NA respectivelyindicate magnification and numerical aperture of a reduction projectionoptical system of a projection aligner.
 44. The pattern formation methodof claim 43, wherein in said photomask, said auxiliary pattern has awidth not less than (0.05×λ×M)/(NA×T^(0.5)) and not more than(0.2×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofsaid auxiliary pattern to said transparent portion.
 45. The patternformation method of claim 43, wherein in said photomask, said auxiliarypattern has a center line thereof in a position away from the center ofsaid transparent portion by a distance not less than (0.365×λ×M)/NA andnot more than (0.435×λ×M)/NA.
 46. The pattern formation method of claim43, wherein in said photomask, said transparent portion has arectangular, polygonal or circular shape.
 47. The pattern formationmethod of claim 43, wherein in said photomask, said auxiliary patternconsists of four rectangular patterns.
 48. The pattern formation methodof claim 43, wherein in said photomask, a transmittance of saidsemi-shielding portion is 3% or more and 15% or less with respect tosaid exposing light.
 49. The pattern formation method of claim 43,wherein in said photomask, a transmittance of said auxiliary patternwith respect to said exposing light is larger than at least thetransmittance of said semi-shielding portion.
 50. The pattern formationmethod of claim 43, wherein in said photomask, a transmittance of saidauxiliary pattern with respect to said exposing light is equivalent to atransmittance of said transparent portion.
 51. The pattern formationmethod of claim 43, wherein in said photomask, said transparent portionis formed by exposing said transparent substrate, said auxiliary patternis formed by depositing, on said transparent substrate, a first phaseshift film that causes, in the exposing light, a phase difference in anopposite phase with respect to said transparent portion, and saidsemi-shielding portion is formed by depositing, on said first phaseshift film, a second phase shift film that causes, in the exposinglight, a phase difference in an opposite phase with respect to saidfirst phase shift film.
 52. The pattern formation method of claim 43,wherein in said photomask, said transparent portion is formed byexposing said transparent substrate, said auxiliary pattern is formed bytrenching said transparent substrate by a depth for causing, in theexposing light, a phase difference in an opposite phase with respect tosaid transparent portion, and said semi-shielding portion is formed bydepositing, on said transparent substrate, a semi-shielding film thattransmits the exposing light in an identical phase with respect to saidtransparent portion.
 53. The pattern formation method of claim 43,wherein in said photomask, said transparent portion is formed byexposing said transparent substrate, said auxiliary pattern is formed bytrenching said transparent substrate by a depth for causing, in theexposing light, a phase difference in an opposite phase with respect tosaid transparent portion, and said semi-shielding portion is formed bydepositing, on said transparent substrate, a metal thin film thattransmits the exposing light in an identical phase with respect to saidtransparent portion.
 54. The pattern formation method of claim 43,wherein in said photomask, said auxiliary pattern is formed by exposingsaid transparent substrate, said transparent portion is formed bytrenching said transparent substrate by a depth for causing, in theexposing light, a phase difference in an opposite phase with respect tosaid auxiliary pattern, and said semi-shielding portion is formed bydepositing, on said transparent substrate, a phase shift film thatcauses, in the exposing light, a phase difference in an opposite phasewith respect to said auxiliary pattern.
 55. The pattern formation methodof claim 43, wherein oblique incident illumination is employed in thestep (b).
 56. A pattern formation method using a photomask, comprisingthe steps of: (a) forming a resist film on a substrate; (b) irradiatingsaid resist film with the exposing light through said photomask, and (c)forming a resist pattern by developing said resist film afterirradiation with the exposing light, wherein said photomask comprises,on a transparent substrate: a semi-shielding portion having atransmitting property against exposing light; a transparent portionsurrounded with said semi-shielding portion and having a transmittingproperty against the exposing light; and an auxiliary pattern surroundedwith said semi-shielding portion and provided around said transparentportion, wherein part of said semi-shielding portion is interposedbetween said transparent portion and said auxiliary pattern, saidtransparent portion is in the shape of a line with a width in a shortside direction smaller than (0.65×λ×M)/NA, said auxiliary pattern is arectangular pattern and has a center line thereof in a position awayfrom the center of said transparent portion by a distance not less than(0.25×λ×M)/NA and not more than (0.45×λ×M)/NA, said semi-shieldingportion and said transparent portion transmit the exposing light in anidentical phase with respect to each other, said auxiliary patterntransmits the exposing light in an opposite phase with respect to saidsemi-shielding portion and said transparent portion and is nottransferred through exposure, and λ indicates a wavelength of theexposing light, and M and NA respectively indicate magnification andnumerical aperture of a reduction projection optical system of aprojection aligner.
 57. The pattern formation method of claim 56,wherein in said photomask, said transparent portion has a longitudinaldimension of (2×λ×M)/NA or more.
 58. The pattern formation method ofclaim 56, wherein in said photomask, said auxiliary pattern has a widthnot less than (0.05×λ×M)/(NA×T^(0.5)) and not more than(0.2×λ×M)/(NA×T^(0.5)), wherein T indicates relative transmittance ofsaid auxiliary pattern to said transparent portion.
 59. The patternformation method of claim 56, wherein in said photomask, said auxiliarypattern has a center line thereof in a position away from the center ofsaid transparent portion by a distance not less than (0.275×λ×M)/NA andnot more than (0.425×λ×M)/NA.
 60. The pattern formation method of claim56, wherein in said photomask, said auxiliary pattern is disposed inparallel to said transparent portion along a line direction of saidtransparent portion, and said transparent portion has a line endprotruded beyond said auxiliary pattern by a given or larger dimensionalong the line direction.
 61. The pattern formation method of claim 56,wherein oblique incident illumination is employed in the step (b).
 62. Apattern formation method using a photomask, comprising the steps of: (a)forming a resist film on a substrate; (b) irradiating said resist filmwith the exposing light through said photomask, and (c) forming a resistpattern by developing said resist film after irradiation with theexposing light, wherein said photomask comprises, on a transparentsubstrate: a semi-shielding portion having a transmitting propertyagainst exposing light; a first transparent portion surrounded with saidsemi-shielding portion and having a transmitting property against theexposing light; an auxiliary pattern surrounded with said semi-shieldingportion and provided around said first transparent portion, and a secondtransparent portion surrounded with said semi-shielding portion andhaving a transmitting property against the exposing light, wherein partof said semi-shielding portion is interposed between said firsttransparent portion and said auxiliary pattern, said auxiliary patternincludes a first auxiliary pattern disposed in an area sandwichedbetween said first transparent portion and said second transparentportion and a second auxiliary pattern disposed in the other area, saidsemi-shielding portion and said first and second transparent portionstransmit the exposing light in an identical phase with respect to eachother, and said auxiliary pattern transmits the exposing light in anopposite phase with respect to said semi-shielding portion and saidfirst and second transparent portions and is not transferred throughexposure.
 63. The pattern formation method of claim 62, wherein in saidphotomask, said first auxiliary pattern is adjacent to a differentauxiliary pattern spaced by a given or smaller distance with saidsemi-shielding portion sandwiched therebetween, said second auxiliarypattern is not adjacent to a different auxiliary pattern spaced by saidgiven or smaller distance with said semi-shielding portion sandwichedtherebetween, and said first auxiliary pattern has a smaller width thansaid second auxiliary pattern.
 64. The pattern formation method of claim62, wherein in said photomask, said first transparent portion is smallerthan a rectangle with a side of (0.8×λ×M)/NA, wherein λ indicates awavelength of the exposing light, and M and NA respectively indicatemagnification and numerical aperture of a reduction projection opticalsystem of a projection aligner.
 65. The pattern formation method ofclaim 62, wherein in said photomask, said first transparent portion isin the shape of a line with a width in a short side direction smallerthan (0.65×λ×M)/NA, wherein λ indicates a wavelength of the exposinglight, and M and NA respectively indicate magnification and numericalaperture of a reduction projection optical system of a projectionaligner.
 66. The pattern formation method of claim 62, wherein obliqueincident illumination is employed in the step (b).